PART III.. Freshwater Polyzoa

FRESHWATER POLYZOA

(CTENOSTOMATA & PHYLACTOLÆMATA).

INTRODUCTION TO PART III.

STATUS AND STRUCTURE OF THE POLYZOA.

The Polyzoa constitute a class in the third great division of the animal kingdom, the so-called Triploblastea. In this division are included also the worms, molluscs, insects, crustacea, spiders, vertebrates, etc.; for heterogeneous as its elements appear, all these animals may be considered to have essential features in common, in particular a body consisting primarily of three cellular layers. Most of them also possess a body cavity distinct from the alimentary canal. Some authors regard the position of the polyzoa as near that of the higher worms, but the group is an isolated one.

In considering the anatomy of simple forms of animal life such as the sponges it is necessary to pay attention mainly to individual cells, but in discussing more complicated forms our notice is first attracted to tissues and organs, for the cells of which these tissues and organs are composed have each a definite position, a definite structure, and a definite function. The most characteristic feature of the polyzoa, considered from this point of view, is the fact that most of their organs fall into one of two categories and are connected either with what is called the "zooecium" or with what is known as the "polypide." The zooecium is a cage in which the polypide is enclosed, but it is a living cage, differing from the shell of a snail or the tubes in which many worms encase themselves in being part of the animal itself. The polypide consists mainly of the organs connected directly and indirectly with nutrition and of part of the muscular system; its name is derived from the fact that it bears a superficial resemblance to a polyp such as Hydra.

The shape and structure of the zooecium differs greatly in different groups of polyzoa. In its simplest form it is merely a cylindrical tube of living matter which secretes an outer horny or gelatinous covering. It is open at the end furthest from its base, at which it is attached either to another zooecium or to some kind of supporting structure. Certain parts of the polypide can always be extruded from the aperture, which is known technically as the "orifice," or withdrawn through it into the zooecium. When the polypide is retracted it draws in with it a portion of the zooecium. The dead outer layer or ectocyst lines part of the portion thus invaginated and forms the walls of a cavity within the orifice. The base of this cavity consists in many forms of a transverse partition pierced in the middle by a circular hole and known as the "diaphragm." The diaphragm, however, does not constitute the limit of the invaginated portion of the zooecium, for the living inner wall or endocyst is dragged in still further and forms a sheath round the retracted tentacles. When the tentacles are protruded they emerge through the hole in the diaphragm, carrying with them their sheath of endocyst. The invagination above the diaphragm, consisting of both endocyst and ectocyst, is then everted.

The tentacles are a characteristic feature of the polypide. Together with the base to which they are attached they are known as the "lophophore"; they surround the mouth, usually in a circle. They differ widely from the tentacles of Hydra in both structure and function, although they too serve as organs for the capture of prey; they are not highly contractile and are not provided with nettle-cells but are covered with cilia, which are in constant motion. When extruded they form a conspicuous calix-like crown to the zooecium, but in the retracted condition they are closely pressed together and lie parallel to one another. They are capable individually of motion in all directions but, although they usually move in concert, they cannot as a rule seize objects between them.

The mouth is a hole situated in the midst of the tentacles. It leads directly into a funnel-shaped oesophagus, the upper part of which is lined with cilia and is sometimes distinguished as the "pharynx," while the lower part, the oesophagus proper, is a thin-walled tube that connects the pharynx with the stomach, which it enters on the dorsal side. The stomach is a bulky organ that differs markedly in form and structure in different groups of polyzoa. It is lined internally with glandular cells and the inner wall is sometimes thrown into folds or "rugæ." The part with which the oesophagus communicates is known as the "cardiac" portion, while the part whence the intestine originates is called the "pylorus" or "pyloric" portion. The intestine commences on the ventral side opposite the entrance of the oesophagus and nearly on a level with it, the bulk of the stomach depending between the two tubes. This part of the stomach is often produced into a blind tube, the fundus or cæcum. The alimentary canal may therefore be described as distinctly Y-shaped. The proximal part of the intestine is in some forms lined with cilia, and the tube as a whole is usually divided into two parts--the intestine proper, which is nearest the stomach, and the rectum, which opens by the anus not far from the mouth.

The nervous system consists of a central ganglion or brain, which is situated at the base of the tentacles on the side nearest the anus and gives out radiating nerves in all directions. Close to the brain and providing a communication between the cavity of the zooecium and the cavity in which the tentacles are contained (or, in the case of an expanded polyp, the external world) is a ciliated tube known as the "intertentacular organ." Apparently it acts as a passage through which the genital products are expelled; but contradictory statements have been made regarding it, and perhaps it is present only at certain seasons or in certain conditions of the polypide.

A=orifice; B=contracted collar; C=diaphragm; D=parieto-vaginal muscles; E=tentacles; F=pharynx; G=oesophagus; H=stomach; J=intestine; K=rectum; L=intertentacular organ; M=retractor muscle; N=testes; O=ovary; P=funiculus; Q=parietal muscles; R=ectocyst; S=endocyst.]

The muscular system is often of a complicated nature, but three sets of muscles may be distinguished as being of peculiar importance, viz., (i) the retractor muscles, which are fixed to the base of the lophophore at one end and to the base of the zooecium at the other, and by contracting pull the former back into the zooecium; (ii) the parieto-vaginal muscles, which connect the upper part of the invaginated portion of the zooecium with the main wall thereof; and (iii) the parietal muscles, which run round the inner wall of the zooecium and compress the zooecium as a whole. The parietal muscles are not developed in the Phylactolæmata, the most highly specialized group of freshwater polyzoa.

The cavity between the polypide and the zooecium contains a reticulate tissue of cells known as the "funicular" tissue, and this tissue is usually concentrated to form a hollow strand or strands ("funiculi") that connect the outer wall of the alimentary canal with the endocyst.

This rapid sketch of the general anatomy of a simple polyzoon will be the best understood by comparing it with fig. 30, which represents, in a somewhat diagrammatic fashion, a vertical section through a single zooecium and polypide of the order Ctenostomata, to which some of the freshwater species belong. The polypide is represented in a retracted condition in which the Y-shaped disposition of the alimentary canal is somewhat obscured.

In the great majority of cases the polyzoa form permanent colonies or polyparia, each of which consists of a number of individual zooecia and polypides connected together by threads of living tissue. These colonies are formed by budding, not by independent individuals becoming associated together. In a few cases compound colonies are formed owing to the fact that separate simple colonies congregate and secrete a common investment; but in these cases there is no organic connection between the constituent colonies. It is only in the small subclass Entoprocta, the polypides and zooecia of which are not nearly so distinct from one another as they are in other polyzoa (the Ectoprocta), that mature solitary individuals occur.

As representatives of both subclasses of polyzoa and of more than one order of Ectoprocta occur in fresh water, I have prefaced my description of the Indian species with a synopsis of the more conspicuous characters of the different groups (pp. 183-186).

CAPTURE AND DIGESTION OF FOOD: ELIMINATION OF WASTE PRODUCTS.

The food of all polyzoa consists of minute living organisms, but its exact nature has been little studied as regards individual species and genera. In Victorella bengalensis it consists largely of diatoms, while the species of Hislopia and Arachnoidea possess an alimentary canal modified for the purpose of retaining flagellate organisms until they become encysted. Similar organisms form a large part of the food of the phylactolæmata.

Although the tentacles may be correctly described as organs used in capturing prey, they do not themselves seize it but waft it by means of the currents set up by their cilia to the mouth, into which it is swept by the currents produced by the cilia lining the pharynx. The tentacles are also able in some species to interlace themselves in order to prevent the escape of prey. Apparently they have the power of rejecting unsuitable food, for they may often be observed to bend backwards and forwards and thrust particles that have approached them away, and if the water contains anything of a noxious nature in solution the lophophore is immediately retracted, unless it has been completely paralysed. In the phylactolæmata the peculiar organ known as the epistome is capable of closing the mouth completely, and probably acts as an additional safeguard in preventing the ingestion of anything of an injurious nature.

In many genera and larger groups the food commonly passes down the pharynx into the stomach without interruption, although it is probable that in all species the oesophagus can be closed off from the stomach by a valve at its base. In some forms, however, a "gizzard" is interposed between the oesophagus and the stomach. This gizzard has not the same function in all cases, for whereas in some forms (e. g., in Bowerbankia) it is lined with horny projections and is a powerful crushing organ, in others (e. g., in Hislopia or Victorella) it acts as an antechamber in which food can be preserved without being crushed until it is required for digestion, or rough indigestible particles can be retained which would injure the delicate walls of the stomach.

Digestion takes place mainly in the stomach, the walls of which are of a glandular nature. The excreta are formed into oval masses in the rectum and are extruded from the anus in this condition.

Although the gross non-nutritious parts of the food are passed per anum, the waste products of the vital processes are not eliminated so easily, and a remarkable process known as the formation of brown bodies frequently takes place. This process cannot be described more clearly and succinctly than by quoting Dr. Harmer's description of it from pp. 471 and 472 of vol. ii. of the Cambridge Natural History, a volume to which I have been much indebted in the preparation of this introduction. The description is based very largely on Dr. Harmer's own observations.

"The tentacles, alimentary canal, and nervous system break down, and the tentacles cease to be capable of being protruded. The degenerating organs become compacted into a rounded mass, known from its colour as the 'brown body.' This structure may readily be seen in a large proportion of the zooecia of transparent species. In active parts of the colony of the body-wall next develops an internal bud-like structure, which rapidly acquires the form of a new polypide. This takes the place originally occupied by the old polypide, while the latter may either remain in the zooecium in the permanent form of a 'brown body,' or pass to the exterior. In Flustra the young polypide-bud becomes connected with the 'brown body' by a funiculus. The apex of the blind pouch or 'cæcum' of the young stomach is guided by this strand to the 'brown body,' which it partially surrounds. The 'brown body' then breaks up, and its fragments pass into the cavity of the stomach, from which they reach the exterior by means of the anus."

Brown bodies are rarely if ever found in the phylactolæmata, in which the life of the colony is always short; but they are not uncommon in Hislopia and Victorella, although in the case of the former they may easily escape notice on account of the fact that they are much paler in colour than is usually the case. When they are found in a ctenostome the collar-like membrane characteristic of the suborder is extruded from the orifice (which then disappears) and remains as a conspicuous external addition to the zooecium, the ectocyst of which, at any rate in Bowerbankia and Victorella, sometimes becomes thickened and dark in colour.

It is noteworthy that the colouring matter of the brown bodies is practically the only colouring matter found in the polypides of most polyzoa. Young polypides are practically colourless in almost all cases.

REPRODUCTION: BUDDING.

Polyzoa reproduce their species in three ways--(i) by means of eggs, (ii) by budding, and (iii) by means of bodies developed asexually and capable of lying dormant in unfavourable conditions without losing their vitality.

Most, if not all species are hermaphrodite, eggs and spermatozoa being produced either simultaneously or in succession by each individual, or by certain individuals in each zoarium. The reproductive organs are borne on the inner surface of the endocyst, as a rule in a definite position, and often in connection with the funiculus or funiculi. It is doubtful to what extent eggs are habitually fertilized by spermatozoa of the individual that has borne them, but in some cases this is practically impossible and spermatozoa from other individuals must be introduced into the zooecium.

Budding as a rule does not result in the formation of independent organisms, but is rather comparable to the proliferation that has become the normal method of growth in sponges, except of course that individuality is much more marked in the component parts of a polyzoon colony than it is in a sponge. In the genera described in this volume budding takes place by the outgrowth of a part of the body-wall and the formation therein of a new polypide, but the order in which the buds appear and their arrangement in reference to the parent zooecium is different in the different groups. In the freshwater ctenostomes three buds are typically produced from each zooecium, one at the anterior end and one at either side, the two latter being exactly opposite one another. The parent zooecium in this formation arises from another zooecium situated immediately behind it, so that each zooecium, except at the extremities of the zoarium, is connected with four other zooecia, the five together forming a cross. The two lateral buds are, however, frequently suppressed, or only one of them is developed, and a linear series of zooecia with occasional lateral branches is formed instead of a series of crosses. In the phylactolæmata, on the other hand, the linear method of budding is the typical one, but granddaughter-buds are produced long before the daughter-buds are mature, so that the zooecia are frequently pressed together, and lateral buds are produced irregularly. In Victorella additional adventitious buds are produced freely near the tip of the zooecium.

Reproduction by spontaneous fission sometimes occurs, especially in the Lophopinæ, but the process differs from that which takes place when a Hydra divides into two, for there is no division of individual zooecia or polypides but merely one of the whole zoarium.

The production of reproductive bodies analogous to the gemmules of sponges appears to be confined in the polyzoa to the species that inhabit fresh or brackish water, nor does it occur in all of these.

All the phylactolæmata produce, within their zooecia, the bodies known as statoblasts. These bodies consist essentially of masses of cells containing abundant food-material and enclosed in a capsule with thick horny walls. In many cases the capsule is surrounded by a "swim-ring" composed of a mass of horny-walled chambers filled with air, which renders the statoblast extremely light and enables it to float on the surface of the water; while in some genera the margin of the swim-ring bears peculiar hooked processes, the function of which is obscure. The whole structure first becomes visible as a mass of cells (the origin of all of which is not the same) formed in connection with the funiculus, and the statoblast may be regarded as an internal bud. Its origin and development in different genera has been studied by several authors, notably by Oka in Pectinatella, and by Braem in Cristatella.

The external form of the statoblasts is very important in the classification of the phylactolæmata, to which these structures are confined. In all the genera that occur in India they are flattened and have an oval, circular, or approximately oval outline.

In temperate climates statoblasts are produced in great profusion at the approach of winter, but in India they occur, in most species, in greatest numbers at the approach of the hot weather.

In the family Paludicellidæ (ctenostomata) external buds which resemble the statoblasts in many respects are produced at the approach of unfavourable climatic conditions, but no such buds are known in the family Hislopiidæ, the zoaria of which appear to be practically perennial. The buds consist of masses of cells formed at the points at which ordinary buds would naturally be produced, but packed with food-material and protected like statoblasts by a thick horny coat. It seems also that old zooecia and polypides are sometimes transformed into buds of the kind (fig. 31), and it is possible that there is some connection between the formation of brown bodies and their production. Like the statoblasts of the phylactolæmata the resting buds of the Paludicellidæ are produced in Europe at the approach of winter, and in India at that of the hot weather.

DEVELOPMENT.

(a) From the Egg.

Some polyzoa are oviparous, while in others a larva is formed within the zooecium and does not escape until it has attained some complexity of structure. Both the ctenostomatous genera that are found in fresh water in India are oviparous, but whereas in Victorella the egg is small and appears to be extruded soon after its fertilization, in Hislopia it remains in the zooecium for a considerable time, increases to a relatively large size, and in some unknown manner accumulates a considerable amount of food-material before escaping. Unfortunately the development is unknown in both genera.

In the phylactolæmata the life-history is much better known, having been studied by several authors, notably by Allman, by Kraepelin, and by Braem (1908). The egg is contained in a thin membrane, and while still enclosed in the zooecium, forms by regular division a hollow sphere composed of similar cells. This sphere then assumes an ovoid form, becomes covered with cilia externally, and breaks its way through the egg-membrane into the cavity of the zooecium. Inside the embryo, by a process analogous to budding, a polypide or a pair of polypides is formed. Meanwhile the embryo has become distinctly pear-shaped, the polypide or polypides being situated at its narrow end, in which a pore makes its appearance. The walls are hollow in the region occupied by the polypide, the cavity contained in them being bridged by slender threads of tissue. The larva thus composed makes its way out of the zooecium, according to Kraepelin through the orifice of a degenerate bud formed for its reception, and swims about for a short time by means of the cilia with which it is covered. Its broad end then affixes itself to some solid object, the polypide is everted through the pore at the narrow end and the whole of that part of the larva which formerly enclosed it is turned completely inside out. A zoarium with its included polypides is finally produced from the young polypide by the rapid development of buds.

(b) From the Statoblast and Resting Buds.

There is little information available as regards the development of the young polyzoon in the resting buds of the freshwater ctenostomes. In Paludicella and Pottsiella the capsule of the bud splits longitudinally into two valves and the polypide emerges between them; but in Victorella bengalensis one of the projections on the margin of the bud appears to be transformed directly into the tip of a new zooecium and the capsule is gradually absorbed.

Contradictory statements have been made as regards several important points in the development of the statoblast and it is probable that considerable differences exist in different species. The following facts appear to be of general application. The cellular contents of the capsule consist mainly of a mass of cells packed with food-material in a granular form, the whole enclosed in a delicate membrane formed of flat cells. When conditions become favourable for development a cavity appears near one end of the mass and the cells that form its walls assume a columnar form in vertical section. The cavity increases rapidly in size, and, as it does so, a young polypide is budded off from its walls. Another bud may then appear in a similar fashion, and the zooecium of the first bud assumes its characteristic features. The capsule then splits longitudinally into two disk-like valves and the young polypide, in some cases already possessing a daughter bud, emerges in its zooecium, adheres by its base to some external object and produces a new polyparium by budding. The two valves of the statoblast often remain attached to the zoarium that has emerged from between them until it attains considerable dimensions (see Plate IV, fig. 3 a).

What conditions favour development is a question that cannot yet be answered in a satisfactory manner. Statoblasts can lie dormant for months and even for years without losing their power of germinating, and it is known that in Europe they germinate more readily after being subjected to a low temperature. In tropical India this is, of course, an impossible condition, but perhaps an abnormally high temperature has the same effect. At any rate it is an established fact that whereas the gemmules of most species germinate in Europe in spring, in Bengal they germinate either at the beginning of the "rains" or at that of our mild Indian winter.

MOVEMENTS.

In the vast majority of the polyzoa, marine as well as freshwater, movement is practically confined to the polypide, the external walls of the zooecium being rigid, the zooecia being closely linked together and the whole zoarium permanently fixed to some extraneous object. In a few freshwater species belonging to the genera Cristatella, Lophopus, Lophopodella and Pectinatella, the whole zoarium has the power of progression. This power is best developed in Cristatella, which glides along with considerable rapidity on a highly specialized "sole" provided with abundant mucus and representing all that remains of the ectocyst. It is by no means clear how the zoaria of the other genera move from one place to another, for the base is not modified, so far as can be seen, for the purpose, and the motion is extremely slow. It is probable, however, that progression is effected by alternate expansions and contractions of the base, and in Lophopodella (fig. 32), which moves rather less slowly than its allies, the anterior part of the base is raised at times from the surface along which it is moving. The whole zoarium can be released in this way and occasionally drops through the water, and is perhaps carried by currents from one place to another in so doing.

So far as the polypides are concerned, the most important movements are those which enable the lophophore and the adjacent parts to be extruded from and withdrawn into the zooecium. The latter movement is executed by means of the retractor muscles, which by contracting drag the extruded parts back towards the posterior end of the endocyst, but it is not by any means certain how the extrusion of the lophophore is brought about. In most ctenostomes the action of the parietal muscles doubtless assists in squeezing it out when the retractor and parieto-vaginal muscles relax, but Oka states that protrusion can be effected in the phylactolæmata even after the zooecium has been cut open. Possibly some hydrostatic action takes place, however, and allowance must always be made for the natural resilience of the inverted portion of the ectocyst.

Even when the polypide is retracted, muscular action does not cease, for frequent movements, in some cases apparently rhythmical, of the alimentary canal may be observed, and in Hislopia contraction of the gizzard takes place at irregular intervals.

When the lophophore is expanded, the tentacles in favourable circumstances remain almost still, except for the movements of their cilia; but if a particle of matter too large for the mouth to swallow or otherwise unsuitable is brought by the currents of the cilia towards it, individual tentacles can be bent down to wave it away and similar movements are often observed without apparent cause.

In the cheilostomes certain individuals of each zoarium are often profoundly modified in shape and function and exhibit almost constant rhythmical or convulsive movements, some ("avicularia") being shaped like a bird's beak and snapping together, others ("vibracula") being more or less thread-like and having a waving motion.

DISTRIBUTION OF THE FRESHWATER POLYZOA.

Fifteen genera of freshwater Polyzoa are now recognized, one entoproctous and fourteen ectoproctous; five of the latter are ctenostomatous and nine phylactolæmatous. Of the fourteen ectoproctous genera seven are known to occur in India, viz., Victorella, Hislopia, Fredericella, Plumatella, Stolella, Lophopodella, and Pectinatella. Except Stolella, which is only known from northern India, these genera have an extremely wide geographical range; Victorella occurs in Europe, India, Africa, and Australia; Hislopia in India, Indo-China, China, and Siberia; Fredericella in Europe, N. America, Africa, India, and Australia; Plumatella in all geographical regions; Lophopodella in E. and S. Africa, India, and Japan; Pectinatella in Europe, N. America, Japan, and India.

Two genera, Paludicella and Lophopus, have been stated on insufficient grounds to occur in India. The former is known from Europe and N. America, and is said to have been found in Australia, while the latter is common in Europe and N. America and also occurs in Brazil.

Of the genera that have not been found in this country the most remarkable are Urnatella and Cristatella. The former is the only representative in fresh water of the Entoprocta and has only been found in N. America. Each individual is borne upon a segmented stalk the segments of which are enclosed in strong horny coverings and are believed to act as resting buds. Cristatella, which is common in Europe and N. America, is a phylactolæmatous genus of highly specialized structure. It possesses a creeping "sole" or organ of progression at the base of the zoarium.

The other phylactolæmatous genera that do not occur in India appear to be of limited distribution, for Australella is only known from N. S. Wales, and Stephanella from Japan. The ctenostomatous Arachnoidea has only been reported from Lake Tanganyika, and Pottsiella only from a single locality in N. America.

As regards the exotic distribution of the Indian species little need be said. The majority of the Plumatellæ are identical with European species, while the only species of Fredericella that has been discovered is closely allied to the European one. The Indian species of Lophopodella occurs also in E. Africa and Japan, while that of Pectinatella is apparently confined to India, Burma and Ceylon, but is closely allied to a Japanese form.

POLYZOA OF BRACKISH WATER.

With the exception of Victorella, which occurs more commonly in brackish than in fresh water and has been found in the sea, the genera that occur in fresh water are confined or practically confined to that medium; but certain marine ctenostomes and cheilostomes not uncommonly make their way, both in Europe and in India, into brackish water, and in the delta of the Ganges an entoproctous genus also does so. The ctenostomatous genera that are found occasionally in brackish water belong to two divisions of the suborder, the Vesicularina and the Alcyonellea. To the former division belongs Bowerbankia, a form of which (B. caudata subsp. bengalensis, p. 187) is often found in the Ganges delta with Victorella bengalensis. No species of Alcyonellea has, however, as yet been found in Indian brackish waters. The two Indian cheilostomes of brackish water belong to a genus (Membranipora) also found in similar situations in Europe. One of them (M. lacroixii) is, indeed, identical with a European form that occurs in England both in the sea and in ditches of brackish water. I have found it in the Cochin backwaters, in ponds of brackish water at the south end of the Chilka Lake (Ganjam, Madras), on the shore at Puri in Orissa, and in the Mutlah River at Port Canning. The second species (M. bengalensis, Stoliczka) is peculiar to the delta of the Ganges and has not as yet been found in the open sea. The two species are easily recognized from one another, for whereas the lip of M. bengalensis (fig. 33) bears a pair of long forked spines, there are no such structures on that of M. lacroixii, the dorsal surface of which is remarkably transparent. M. lacroixii forms a flat zoarium, the only part visible to the naked eye being often the beaded margin of the zooecia, which appears as a delicate reticulation on bricks, logs of wood, the stems of rushes and of hydroids, etc.; but the zoarium of M. bengalensis is as a rule distinctly foliaceous and has a peculiar silvery lustre.

Loxosomatoides (fig. 34), the Indian entoproctous genus found in brackish water, has not as yet been obtained from the open sea, but has recently been introduced, apparently from a tidal creek, into isolated ponds of brackish water at Port Canning. It is easily recognized by the chitinous shield attached to the ventral (posterior) surface.

A and B, a single individual of form A, as seen (A) in lateral, and (B) in ventral view; C, outline of a similar individual with the tentacles retracted, as seen from in front (dorsal view); D, ventral view of an individual and bud of form B. All the figures are from the type specimens and are multiplied by about 70.]

II.

HISTORY OF THE STUDY OF THE FRESHWATER POLYZOA.

The naturalists of the eighteenth century were acquainted with more than one species of freshwater polyzoon, but they did not distinguish these species from the hydroids. Trembley discovered Cristatella, which he called "Polype à Panache," in 1741, and Linné described a species of Plumatella under the name Tubipora repens in 1758, while ten years later Pallas gave a much fuller description (under the name Tubularia fungosa) of the form now known as Plumatella fungosa or P. repens var. fungosa. Although Trembley, Baker, and other early writers on the fauna of fresh water published valuable biological notes, the first really important work of a comprehensive nature was that of Dumortier and van Beneden, published in 1848. All previous memoirs were, however, superseded by Allman's Monograph of the Fresh-Water Polyzoa, which was issued in 1857, and this memoir remains in certain respects the most satisfactory that has yet been produced. In 1885 Jullien published a revision of the phylactolæmata and freshwater ctenostomes which is unfortunately vitiated by some curious lapses in observation, but it is to Jullien that the recognition of the proper position of Hislopia is due. The next comprehensive monograph was that of Kraepelin, which appeared in two parts (1887 and 1892) in the Abhandlungen des Naturwiss. Vereins of Hamburg. In its detailed information and carefully executed histological plates this work is superior to any that preceded it or has since appeared, but the system of classification adopted is perhaps less liable to criticism than that followed by Braem in his "Untersuchungen," published in the Bibliotheca Zoologica in 1888.

During the second half of the nineteenth century and the first decade of the twentieth several authors wrote important works on the embryology and anatomy of the phylactolæmata, notably Kraepelin, Braem, and Oka; but as yet the ctenostomes of fresh water have received comparatively little attention from anything but a systematic point of view.

From all points of view both the phylactolæmata and the ctenostomes of Asia have been generally neglected, except in the case of the Japanese phylactolæmata, which have been studied by Oka. Although Carter made some important discoveries as regards the Indian forms, he did not devote to them the same attention as he did to the sponges. In the case of the only new genus he described he introduced a serious error into the study of the two groups by placing Hislopia among the cheilostomes, instead of in its true position as the type genus of a highly specialized family of ctenostomes.

For fuller details as to the history of the study of the freshwater Polyzoa the student may refer to Allman's and to Kraepelin's monographs. An excellent summary is given by Harmer in his chapter on the freshwater Polyzoa in vol. ii. of the Cambridge Natural History; and Loppens has recently (1908) published in the Annales de Biologie lacustre a concise survey of the systematic work that has recently been undertaken. Unfortunately he perpetuates Carter's error as regards the position of Hislopia.

BIBLIOGRAPHY OF THE FRESHWATER POLYZOA.

A very full bibliography of the freshwater Polyzoa will be found in pt. i. of Kraepelin's "Die Deutschen Süsswasserbryozoen" (1887), while Loppens, in his survey of the known species (Ann. Biol. lacustre, ii, 1908), gives some recent references. The following list contains the titles of some of the more important works of reference, of memoirs on special points such as reproduction and of papers that have a special reference to Asiatic species. Only the last section is in any way complete.

(a) Works of Reference.

1847. VAN BENEDEN, "Recherches sur les Bryozoaires fluviatiles de Belgique," Mém. Ac. Roy. Belgique, xxi.

1850. DUMORTIER and VAN BENEDEN, "Histoire Naturelle des Polypes composés d'eau douce," 2^e partie, Mém. Ac. Roy. Bruxelles, xvi (complément).

1856. ALLMAN, "A Monograph of the Fresh-Water Polyzoa" (London).

1866-1868. HYATT, "Observations on Polyzoa, suborder Phylactolæmata," Comm. Essex Inst. iv, p. 197, v, p. 97.

1880. HINCKS, "A History of the British Marine Polyzoa."

1885. JULLIEN, "Monographie des Bryozoaires d'eau douce," Bull. Soc. zool. France, x, p. 91.

1887 & 1892. KRAEPELIN, "Die deutschen Süsswasserbryozoen," Abhandl. Nat. Vereins Hamburg, x & xii.

1890. BRAEM, "Untersuchungen des Bryozoen des süssen Wassers," Bibl. Zool. ii, Heft 6 (Cassel).

1896. HARMER, Cambridge Natural History, ii, Polyzoa, chap. xviii.

1899. KORSCHELT and HEIDER, "Embryology of Invertebrates," vol. ii, chap. xvi. (English edition by Bernard and Woodward, 1899.)

1908. LOPPENS, "Les Bryozoaires d'eau douce," Ann. Biol. lacustre, iii. p. 141.

(b) Special Works on Embryology, etc.

1875. NITSCHE, "Beiträge zur Kenntniss der Bryozoen," Zeitschr. f. wiss. Zool. xxv (supplement), p. 343.

1880. REINHARD, "Zur Kenntniss der Süsswasser-Bryozoen," Zool. Anz. iii, p. 208.

1888. BRAEM, "Untersuchungen über die Bryozoen des süssen Wassers," Zool. Anz. xi, pp. 503, 533.

1891. OKA, "Observations on Freshwater Polyzoa," J. Coll. Sci. Tokyo, iv, p. 89.

1906. WILCOX, "Locomotion in young colonies of Pectinatella magnifica," Biol. Bull. Wood's Hole, ii.

1908. BRAEM, "Die geschlechtliche Entwickelung von Fredericella sultana nebst Beobachtungen über die weitere Lebensgeschichte der Kolonien," Bibl. Zool. xx, Heft 52.

(c) Papers that refer specifically to Asiatic species.

1851. LEIDY described Plumatella diffusa in Proc. Ac. Philad. v, p. 261 (1851).

1858. CARTER, "Description of a Lacustrine Bryozoon allied to Flustra," Ann. Nat. Hist. (3) i, p. 169.

1859. CARTER, "On the Identify in Structure and Composition of the so-called Seed-like Body of Spongilla with the Winter-egg of the Bryozoa: and the presence of Starch-granules in each," Ann. Nat. Hist. (3) iii, p. 331. (Statoblast of Lophopodella described and figured.)

1862. MITCHELL, "Freshwater Polyzoa," Q. J. Micr. Sci. (new series) ii, p. 61. ("Lophopus" recorded from Madras.)

1866. HYATT, "Observations on Polyzoa, suborder Phylactolæmata," Comm. Essex Inst. iv, p. 197. ("Pectinatella carteri" named.)

1869. STOLICZKA, "On the Anatomy of Sagartia schilleriana and Membranipora bengalensis, a new coral and a bryozoon living in brackish water at Port Canning," J. As. Soc. Bengal, xxxviii, ii, p. 28.

1880. JULLIEN, "Description d'un nouveau genre de Bryozoaire Cheilostomien des eaux douces de la Chine et du Cambodge et de deux espèces nouvelles," Bull. Soc. zool. France, v, p. 77. ("Norodonia" described.)

1885. JULLIEN, "Monographie des Bryozoaires d'eau douce," Bull. Soc. zool. France, x, p. 91. (Hislopia assigned to the ctenostomes.)

1887. KRAEPELIN, "Die deutschen Süsswasserbryozoen," Abh. Ver. Hamburg, x. (Plumatella philippinensis.)

1891. OKA, "Observations on Freshwater Polyzoa," J. Coll. Sci. Tokyo, iv, p. 89.

1898. MEISSNER, "Die Moosthiere Ost-Afrikas," in Mobius's Deutsch-Ost-Afrika, iv. (Lophopodella carteri recorded from E. Africa.)

1901. KOROTNEFF, "Faunistische Studien am Baikalsee," Biol. Centrbl. xxi, p. 305. ("Echinella" described.)

1904-1906. ROUSSELET, "On a new Freshwater Polyzoon from Rhodesia, Lophopodella thomasi, gen. et sp. nov.", J. Quekett Club (2) ix, p. 45. (Genus Lophopodella described.)

1906. ANNANDALE, "Notes on the Freshwater Fauna of India. No. II. The Affinities of Hislopia," J. As. Soc. Bengal (new series) ii, p. 59.

1906. KRAEPELIN, "Eine Süsswasser-bryozoë (Plumatella) aus Java," Mitth. Mus. Hamburg, xxiii, p. 143.

1907. ANNANDALE, "Notes on the Freshwater Fauna of India. No. XII. The Polyzoa occurring in Indian Fresh and Brackish Pools," J. As. Soc. Bengal (new series) iii, p. 83.

1907. ANNANDALE, "Statoblasts from the surface of a Himalayan Pond," Rec. Ind. Mus. i, p. 177.

1907. ANNANDALE, "The Fauna of Brackish Ponds at Port Canning, Lower Bengal: I.--Introduction and Preliminary Account of the Fauna," Rec. Ind. Mus. i, p. 35.

1907. ANNANDALE, "The Fauna of Brackish Ponds at Port Canning, Lower Bengal: VI.--Observations on the Polyzoa, with further notes on the Ponds," Rec. Ind. Mus. i, p. 197.

1907. ANNANDALE, "Further Note on a Polyzoon from the Himalayas," Rec. Ind. Mus. i, p. 145.

1907. ROUSSELET, "Zoological Results of the Third Tanganyika Expedition, conducted by Dr. W. A. Cunnington, 1904-1905.--Report on the Polyzoa," P. Z. Soc. London, i, p. 250. (Plumatella tanganyikæ.)

1907. OKA, "Eine dritte Art von Pectinatella (P. davenporti, n. sp.)," Zool. Anz. xxxi, p. 716.

1907. APSTEIN, "Das Plancton im Colombo-See auf Ceylon," Zool. Jahrb. (Syst.) xxv, p. 201. (Plumatella recorded.)

1907. WALTON, "Notes on Hislopia lacustris, Carter," Rec. Ind. Mus. i, p. 177.

1907-1908. OKA, "Zur Kenntnis der Süsswasser-Bryozoenfauna von Japan," Annot. Zool. Japon, vi, p. 117.

1907-1908. OKA, "Ueber eine neue Gattung von Süsserwasserbryozoen," Annot. Zool. Japon, vi, p. 277.

1908. ANNANDALE, "The Fauna of Brackish Ponds at Port Canning, Lower Bengal: VII.--Further Observations on the Polyzoa with the description of a new genus of Entoprocta," Rec. Ind. Mus. ii, p. 11.

1908. ANNANDALE, "Corrections as to the Identity of Indian Phylactolæmata," Rec. Ind. Mus. ii, p. 110.

1908. ANNANDALE, "Three Indian Phylactolæmata," Rec. Ind. Mus. ii, p. 169.

1908. KIRKPATRICK, "Description of a new variety of Spongilla loricata, Weltner," Rec. Ind. Mus. ii, p. 97. (Hislopia recorded from Burma.)

1909. ANNANDALE, "Preliminary Note on a new genus of Phylactolæmatous Polyzoa," Rec. Ind. Mus. iii, p. 279.

1909. ANNANDALE, "A new species of Fredericella from Indian Lakes," Rec. Ind. Mus. iii. p. 373.

1909. WALTON, "Large Colonies of Hislopia lacustris," Rec. Ind. Mus. iii, p. 295.

1910. ANNANDALE, "Materials for a Revision of the Phylactolæmatous Polyzoa of India," Rec. Ind. Mus. v, p. 37.

1911. WEST and ANNANDALE, "Descriptions of Three Species of Algæ associated with Indian Freshwater Polyzoa," J. As. Soc. Bengal (ined.).

GLOSSARY OF TECHNICAL TERMS USED IN PART III.

Brown body A body formed in a zooecium by the degeneration of a polypide as a preparation for its regeneration.

Cardiac portion (of That part which communicates with the the stomach). oesophagus.

Collar A longitudinally pleated circular membrane capable of being thrust out of the orifice in advance of the lophophore and of closing together inside the zooecium above the tentacles when they are retracted.

Dorsal surface (Of zooecium or polypide) the surface nearest the mouth; (of statoblast) the surface furthest from that by which the statoblast is attached to the funiculus during development.

Ectocyst The outer, structureless layer of the zooecium.

Emarginate Having a thin or defective triangular area (of a zooecium) in the ectocyst at the tip.

Endocyst The inner, living (cellular) layer of the zooecium.

Epistome A leaf-like ciliated organ that projects upwards and forwards over the mouth between it and the anus.

Funiculus A strand of tissue joining the alimentary canal to the endocyst.

Furrowed Having a thin or defective longitudinal (of a zooecium) linear streak in the ectocyst on the dorsal surface.

Gizzard A chamber of the alimentary canal situated at the cardiac end of the stomach and provided internally with a structureless lining.

Intertentacular organ A ciliated tube running between the cavity of the zooecium and the external base of the lophophore.

Keeled Having a longitudinal ridge on the dorsal (of a zooecium) surface.

Lophophore The tentacles with the base to which they are attached.

Marginal processes Chitinous hooked processes on the margin (of statoblast). of the swim-ring (q. v.).

OEsophagus That part of the alimentary canal which joins the mouth to the stomach.

Orifice The aperture through which the lophophore can be protruded from or retracted into the zooecium.

Parietal muscles Transverse muscles running round the inner wall of the zooecium.

Parieto-vaginal Muscles that surround the orifice, running muscles between the folds of the zooecium in an oblique direction.

Polyparium The whole body of zooecia and polypides which are in organic connection.

Polypide The tentacular crown, alimentary canal, and retractor muscles of a polyzoon-individual.

Pyloric portion That part which communicates with the (of the stomach). intestine.

Resting bud An external bud provided with food-material in its cells, with a horny external coat and capable of lying dormant in unfavourable conditions.

Retractor muscles The muscles by the action of which the lophophore can be pulled back into the zooecium.

Statoblast An internal bud arising from the funiculus, containing food-material in its cells, covered with a horny coat and capable of lying dormant in unfavourable conditions.

Swim-ring A ring of polygonal air-spaces surrounding the statoblast.

Ventral surface (Of zooecium or polypide) the surface nearest the anus; (of statoblast) the surface by which the statoblast is attached to the funiculus during development.

Zoarium The whole body of zooecia which are in organic connection.

Zooecium Those parts of the polyzoon-individual which constitute a case or "house" for the polypide.

SYNOPSIS OF THE CLASSIFICATION OF THE POLYZOA.

SYNOPSIS OF THE SUBCLASSES, ORDERS, AND SUBORDERS.

Class POLYZOA.

Small coelomate animals, each individual of which consists of a polyp-like organism or polypide enclosed in a "house" or zooecium composed partly of living tissues. The mouth is surrounded by a circle of ciliated tentacles that can be retracted within the zooecium; the alimentary canal, which is suspended in the zooecium, is Y-shaped and consists of three parts, the oesophagus, the stomach, and the intestine.

Subclass ENTOPROCTA.

The anus as well as the mouth is enclosed in the circle of tentacles and the zooecium is not very distinctly separated from the polypide. Some forms are solitary or form temporary colonies by budding.

Most Entoprocta are marine, but a freshwater genus (Urnatella) occurs in N. America, while the Indian genus Loxosomatoides (fig. 34, p. 176) is only known from brackish water.

Subclass ECTOPROCTA.

The anus is outside the circle of tentacles and the zooecium can always be distinguished from the polypide. All species form by budding permanent communities the individuals in which remain connected together by living tissue.

Order I. GYMNOLÆMATA.

Ectoproctous polyzoa the polypides of which have no epistome; the zooecia are in nearly all cases distinctly separated from one another by transverse perforated plates.

Most of the Gymnolæmata are marine, but species belonging to two of the three suborders into which they are divided often stray into brackish water, while a few genera that belong to one of these two suborders are practically confined to fresh water. The three suborders are distinguished as follows:--

Suborder A. CHEILOSTOMATA.

The zooecia are provided with a "lip" or lid hinged to the posterior margin of the orifice (see fig. 33, p. 175). This lid closes automatically outside the zooecium or in a special chamber on the external surface (the "peristome") when the polypide retracts and is pushed open by the tentacles as they expand. The majority of the zooecia in each zoarium are more or less distinctly flattened, but some of them are often modified to form "vibracula" and "avicularia."

The Cheilostomata are essentially a marine group, but some species are found in estuaries and even in pools and ditches of brackish water (fig. 33).

Suborder B. CTENOSTOMATA.

The zooecia are provided with a collar-like membrane which is pleated vertically and closes together above the polypide inside the zooecium when the former is retracted; it is thrust out of the zooecium and expands into a ring-shaped form just before the tentacles are extruded. The zooecia are usually more or less tubular, but in some genera and species are flattened.

The majority of the Ctenostomata are marine, but some genera are found in estuaries, while those of one section of the suborder live almost exclusively in fresh water.

Suborder C. CYCLOSTOMATA.

The zooecia are provided neither with a lip nor with a collar-like membrane. They are tubular and usually have circular orifices.

The Cyclostomata are exclusively marine.

Order II. PHYLACTOLÆMATA.

Ectoproctous polyzoa the polypides of which have a leaf-shaped organ called an epistome projecting upwards and forwards within the circle of tentacles and between the mouth and the anus. The zooecia are not distinct from one another, but in dendritic forms the zoarium is divided irregularly by chitinous partitions.

The Phylactolæmata are, without exception, freshwater species.

II.

SYNOPSIS OF THE LEADING CHARACTERS OF THE DIVISIONS OF THE SUBORDER CTENOSTOMATA.

Suborder B. CTENOSTOMATA.

The suborder has been subdivided in various ways by different authors. The system here adopted is essentially the same as that proposed in a recent paper by Waters (Journ. Linn. Soc. London, Zool. xxi, p. 231, 1910), but I have thought it necessary to add a fourth division to the three adopted by that author, namely, the Alcyonellea, Stolonifera, and Vesicularina. This new division includes all the freshwater genera and may be known as the Paludicellina. In none of these divisions are the tentacles webbed at the base.

The four divisions may be recognized from the following synopsis of their characteristic features:--

Division I. ALCYONELLEA.

The zooecia arise directly from one another in a fleshy or gelatinous mass. The polypide has no gizzard. The species are essentially marine, but a few are found in brackish water in estuaries.

Division II. STOLONIFERA.

The zooecia arise from expansions in a delicate creeping rhizome or root-like structure, the order in which they are connected together being more or less irregular. As a rule (perhaps always) there is no gizzard. The species are marine.

Division III. VESICULARINA.

The zooecia grow directly from a tubular stem which is usually free and vertical, their arrangement being alternate, spiral or irregular. There is a stout gizzard which bears internal chitinous projections and is tightly compressed when the polypide is retracted. The species are essentially marine, but a few are found in brackish water.

Division IV. PALUDICELLINA, nov.

The zooecia are arranged in a regular cruciform manner and arise either directly one from another or with the intervention of tubular processes. If the polypide has a gizzard it does not bear internal chitinous projections. Most of the species are confined to fresh water, but a few are found in brackish water or even in the sea.

Although all true freshwater Ctenostomes belong to the fourth of these divisions, species of a genus (Bowerbankia) included in the third are so frequently found in brackish water and in association with one belonging to the fourth, and are so easily confounded with the latter, that I think it necessary to include a brief description of the said genus and of the form that represents it in ponds of brackish water in India.

SYSTEMATIC LIST OF THE INDIAN FRESHWATER POLYZOA.

Order I. GYMNOLÆMATA.

Suborder I. CTENOSTOMATA.

Division IV. Paludicellina, nov.

Family I. PALUDICELLIDÆ.

Genus 1. PALUDICELLA, Gervais (1836).

? Paludicella sp. (fide Carter).

Genus 2. VICTORELLA, Kent (1870).

26.V. bengalensis*, Annandale (1907).

Family II. HISLOPIIDÆ.

Genus HISLOPIA, Carter (1858).

27. H. lacustris, Carter (1858). 27 a. H. lacustris subsp. moniliformis*, nov.

Order II. PHYLACTOLÆMATA.

Division I. Plumatellina.

Family 1. FREDERICELLIDÆ.

Genus FREDERICELLA, Gervais (1836).

28. F. indica*, Annandale (1909).

Family 2. PLUMATELLIDÆ.

Subfamily A. PLUMATELLINÆ.

Genus 1. PLUMATELLA, Lamarck (1816).

29. P. fruticosa, Allman (1844). 30. P. emarginata, Allman (1844). 31. P. javanica*, Kraepelin (1905). 32. P. diffusa, Leidy (1851). 33. P. allmani, Hancock (1850). 34. P. tanganyikæ*, Rousselet (1907). 35. P. punctata, Hancock (1850).

Genus 2. STOLELLA, Annandale (1909).

36. S. indica*, Annandale (1909).

Subfamily B. LOPHOPINÆ.

Genus 1. LOPHOPODELLA, Rousselet (1904).

37. L. carteri* (Hyatt) (1865). 37 a. L. carteri var. himalayana* (Annandale) (1907).

Genus 2. PECTINATELLA, Leidy (1851).

38. P. burmanica*, Annandale (1908).

Order CTENOSTOMATA.

Family VESICULARIDÆ.

VESICULARIDÆ, Hincks, Brit. Marine Polyzoa, p. 512 (1880).

Zooecia constricted at the base, deciduous, attached to a stem that is either recumbent or vertical.

Genus BOWERBANKIA, Farre.

Bowerbankia, Farre, Phil. Trans. Roy. Soc. cxxvii, p. 391 (1837).

Bowerbankia, Hincks, op. cit. p. 518.

Zoarium vertical or recumbent. Zooecia ovate or almost cylindrical, arranged on the stem singly, in clusters or in a subspiral line. Polypide with 8 or 10 tentacles.

Bowerbankia caudata, Hincks.

Bowerbankia caudata, Hincks, op. cit. p. 521, pl. lxxv, figs. 7, 8.

This species is easily distinguished from all others by the fact that mature zooecia have always the appearance of being fixed to the sides of a creeping, adherent stem and are produced, below the point at which they are thus fixed, into a pointed "tail."

Subsp. bengalensis, Annandale.

Bowerbankia caudata, Thornely, Rec. Ind. Mus. i, p. 196 (1907).

Bowerbankia caudata, Annandale, ibid. p. 203.

Bowerbankia caudata race bengalensis, id., ibid. ii. p. 13 (1908).

The Indian race is only distinguished from the typical form by its greater luxuriance of growth and by the fact that the "tail" of the zooecia is often of relatively great length, sometimes equaling or exceeding the rest of the zooecium. The stem, which is divided at irregular intervals by partitions, often crosses and recrosses its own course and even anastomoses, and a fur-like structure is formed in which the zooecia representing the hairs become much elongated; but upright branches are never formed. The zoarium has a greenish or greyish tinge.

TYPE in the Indian Museum.

GEOGRAPHICAL DISTRIBUTION.--B. caudata subsp. bengalensis is common in brackish water in the Ganges delta, where it often occurs in close association with Victorella bengalensis, and also at the south end of the Chilka Lake in the north-east of the Madras Presidency. Although it has not yet been found elsewhere, it probably occurs all round the Indian coasts.]

Division PALUDICELLINA, nov.

This division consists of two very distinct families, the species of which are easily distinguished at a glance by the fact that in one (the Paludicellidæ) the zooecia are tubular, while in the other (the Hislopiidæ) they are broad and flattened. The anatomical and physiological differences between the two families are important, and they are associated together mainly on account of the method of budding by means of which their zoaria are produced.

A, zooecium of Victorella pavida, Kent, with the polypide retracted (after Kraepelin).

B, zooecium of Hislopia lacustris, Carter (typical form from the United Provinces), with the collar completely and the tentacles partly protruded.

A=collar; B=orifice; C=tentacles; D=pharynx; E=oesophagus proper; F=gizzard; G=stomach; G'=cardiac portion of stomach; H=intestine; J=rectum; K=anus; L=young egg; M=green cysts in gizzard; N=testes; O=ovary; O'=funiculus.

The muscles are omitted except in fig. B.]

Family PALUDICELLIDÆ.

PALUDICELLIDÆ, Allman, Mon. Fresh-Water Polyzoa, p. 113 (1857).

HOMODIÆTIDÆ, Kent, Q. J. Micr. Sci. x, p. 35 (1870).

VICTORELLIDÆ, Hincks, Brit. Marine Polyzoa, p. 558 (1880).

PALUDICELLIDÉES, Jullien, Bull. Soc. zool. France, x, p. 174 (1885).

PALUDICELLIDES, Loppens, Ann. Biol. lacustre, iii, p. 170 (1908).

VICTORELLIDES, id., ibid. p. 171.

Zoarium. The zoarium is recumbent or erect, and is formed typically either of zooecia arising directly in cruciform formation from one another, or of zooecia joined together in similar formation with the intervention of tubules arising from their own bases. Complications often arise, however, either on account of the suppression of the lateral buds of a zooecium, so that the formation becomes linear instead of cruciform, or by the production in an irregular manner of additional tubules and buds from the upper part of the zooecia. A confused and tangled zoarium may thus be formed, the true nature of which can only be recognized by the examination of its terminal parts.

Zooecia. The zooecia are tubular and have a terminal or subterminal orifice, which is angulate or subangulate as seen from above. Owing to this fact, to the stiff nature of the external ectocyst, to the action of circular muscles that surround the tentacular sheath, and to the cylindrical form of the soft inverted part, the orifice, as seen from above, appears to form four flaps or valves, thus [illustration: sketch, similar to a cloverleaf inside a square with rounded corners].

Polypide. The alimentary canal is elongate and slender as a whole, the oesophagus (including the pharynx) being of considerable length. In Paludicella and Pottsiella the oesophagus opens directly into the cardiac limb of the stomach, which is distinctly constricted at its base; but in Victorella the base of the oesophagus is constricted off from the remainder to form an elongate oval sac the walls of which are lined with a delicate structureless membrane. Victorella may therefore be said to possess a gizzard, but the structure that must be so designated has not the function (that of crushing food) commonly associated with the name, acting merely as a chamber for the retention of solid particles. In this genus the cardiac limb of the stomach is produced and vertical but not constricted at the base. The tentacles in most species number 8, but in Paludicella there are 16.

Resting buds. The peculiar structures known in Europe as "hibernacula" are only found in this family. The name hibernacula, however, is inappropriate to the only known Indian species as they are formed in this country at the approach of summer instead of, as in Europe and N. America, at that of winter. It is best, therefore, to call them "resting buds." They consist of masses of cells congregated at the base of the zooecia, gorged with food material and covered with a resistant horny covering.

The family Paludicellidæ consists of three genera which may be distinguished as follows:--

I. Orifice terminal; main axis of the zooecium vertical; zooecia separated from one another by tubules. [A. Base of the zooecia not swollen; no adventitious buds POTTSIELLA.] B. Base of the zooecium swollen; adventitious buds produced near the tip VICTORELLA, p. 194. II. Orifice subterminal, distinctly on the dorsal surface; main axis of the zooecium horizontal (the zoarium being viewed from the dorsal surface); buds not produced at the tip of the zooecia PALUDICELLA, p. 192.

Of these three genera, Pottsiella has not yet been found in India and is only known to occur in N. America. It consists of one species, P. erecta (Potts) from the neighbourhood of Philadelphia in the United States.

Victorella includes four species, V. pavida known from England and Germany and said to occur in Australia, V. mülleri from Germany (distinguished by possessing parietal muscles at the tip of the zooecia), V. symbiotica from African lakes and V. bengalensis from India. These species are closely related.

Paludicella is stated by Carter to have been found in Bombay, but probably what he really found was the young stage of V. bengalensis. A single species is known in Europe and N. America, namely P. ehrenbergi, van Beneden (=Alcyonella articulata, Ehrenberg).

I have examined specimens of all the species of this family as yet known.

Genus 1. PALUDICELLA, Gervais.

Paludicella, Gervais, Compt. Rend. iii, p. 797 (1836).

Paludicella, Allman, Mon. Fresh-Water Polyzoa, p. 113 (1857).

? Paludicella, Carter, Ann. Nat. Hist. (3) iii, p. 333 (1859).

Paludicella, Jullien, Bull. Soc. zool. France, x, p. 174 (1885).

Paludicella, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 96 (1887).

Paludicella, Loppens, Ann. Biol. lacustre, iv, p. 14 (1910).

Zoarium. The nature of the zoarium in this genus is well expressed by Ehrenberg's specific name "articulata," although the name was given under a false impression. The zooecia arise directly from one another in linear series with occasional side-branches. The side-branches are, however, often suppressed. The zoarium as a whole is either recumbent and adherent or at least partly vertical.

Zooecia. Although the zooecia are distinctly tubular as a whole, two longitudinal axes may be distinguished in each, for the tip is bent upwards in a slanting direction, bearing the orifice at its extremity. The main axis is, however, at right angles to the dorso-ventral axis, and the dorsal surface, owing to the position of the aperture, can always be readily distinguished from the ventral, even when the position of the zooecium is vertical. Each zooecium tapers towards the posterior extremity. Parietal muscles are always present.

A=a single zooecium with the polypide retracted. B=the base of the lophophore as seen from above with the tentacles removed. C=the orifice of a polypide with the collar expanded and the tentacles partly retracted. a=tentacles; c=collar; d=mouth; e=oesophagus; f=stomach; g=intestine; k=parieto-vaginal muscles; p=parietal muscles; o=cardiac part of the stomach; r=retractor muscle; s=funiculus.]

Polypide. The most striking features of the polypide are the absence of any trace of a gizzard and the highly specialized form assumed by the cardiac part of the stomach. There are two funiculi, both connecting the pyloric part of the stomach with the endocyst. The ovary develops at the end of the upper, the testis at that of the lower funiculus.

Resting buds. The resting buds are spindle-shaped.

Kraepelin recognized two species in the genus mainly by their method of growth and the number of tentacles. In his P. mülleri the zoarium is always recumbent and the polypide has 8 tentacles, whereas in P. articulata or ehrenbergi the tentacles number 16 and upright branches are usually developed. It is probable, however, that the former species should be assigned to Victorella, for it is often difficult to distinguish Paludicella from young specimens of Victorella unless the latter bear adventitious terminal buds. The gizzard of Victorella can be detected in well-preserved material even under a fairly low power of the microscope, and I have examined specimens of what I believe to be the adult of mülleri which certainly belong to that genus.

It is always difficult to see the collar of Paludicella, because of its transparency and because of the fact that its pleats are apparently not strengthened by chitinous rods as is usually the case. Allman neither mentions it in his description of the genus nor shows it in his figures, and Loppens denies its existence, but it is figured by Kraepelin and can always be detected in well-preserved specimens, if they are examined carefully. If the collar were actually absent, its absence would separate Paludicella not only from Victorella and Pottsiella, but also from all other ctenostomes. In any case, Victorella is distinguished from Paludicella and Pottsiella by anatomical peculiarities (e. g., the possession of a gizzard and the absence of a second funiculus) that may ultimately be considered sufficiently great to justify its recognition as the type and only genus of a separate family or subfamily.

The description of Paludicella is included here on account of Carter's identification of the specimens he found at Bombay; but its occurrence in India is very doubtful.

Genus 2. VICTORELLA, Kent.

Victorella, Kent, Q. J. Micr. Sci. x, p. 34 (1870).

Victorella, Hincks, Brit. Marine Polyzoa, p. 559 (1880).

Victorella, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 93 (1887).

TYPE, Victorella pavida, Kent.

Zoarium. The zoarium consists primarily of a number of erect or semi-erect tubular zooecia joined together at the base in a cruciform manner by slender tubules, but complications are introduced by the fact that adventitious buds and tubules are produced, often in large numbers, round the terminal region of the zooecia, and that these buds are often separated from their parent zooecium by a tubule of considerable length, and take root among other zooecia at a distance from their point of origin. A tangled mass may thus be formed in which it is difficult to recognize the regular arrangement of the zooecia that can be readily detached at the growing points of the zoarium.

Zooecia. The zooecia when young closely resemble those of Paludicella, but as they grow the terminal upturned part increases rapidly, while the horizontal basal part remains almost stationary and finally appears as a mere swelling at the base of an almost vertical tube, in which by far the greater part, if not the whole, of the polypide is contained. Round the terminal part of this tube adventitious buds and tubules are arranged more or less regularly. There are no parietal muscles.

Polypide. The polypide has 8 slender tentacles, which are thickly covered with short hairs. The basal part of the oesophagus forms a thin-walled sac (the "gizzard") constricted off from the upper portion and bearing internally a thin structureless membrane. Circular muscles exist in its wall but are not strongly developed on its upper part. There is a single funiculus, which connects the posterior end of the stomach with the base of the zooecium. The ovaries and testes are borne on the endocyst, not in connection with the funiculus.

Resting buds. The resting buds are flattened or resemble young zooecia in external form.

Victorella, although found in fresh water, occurs more commonly in brackish water and is known to exist in the littoral zone of the sea.

26. Victorella bengalensis, Annandale.

Victorella pavida, Annandale (nec Kent), Rec. Ind. Mus. i, p. 200, figs. 1-4 (1907).

Victorella bengalensis, id., ibid. ii, p. 12, fig. 1 (1908).

Zoarium. The mature zoarium resembles a thick fur, the hairs of which are represented by elongate, erect, slender tubules (the zooecia), the arrangement of the whole being very complicated and irregular. The base of the zoarium often consists of an irregular membrane formed of matted tubules, which are sometimes agglutinated together by a gummy secretion. The zoarium as a whole has a faint yellowish tinge.

Zooecia. The zooecia when young are practically recumbent, each being of an ovoid form and having a stout, distinctly quadrate orificial tubule projecting upwards and slightly forwards near the anterior margin of the dorsal surface. At this stage a single tubule, often of great relative length, is often given off near the orifice, bearing a bud at its free extremity. As the zooecium grows the tubular part becomes much elongated as compared with the basal part and assumes a vertical position. Its quadrate form sometimes persists but more often disappears, so that it becomes almost circular in cross-section throughout its length. Buds are produced near the tip in considerable profusion. As a rule, if they appear at this stage, the tubule connecting them with the parent zooecium is short or obsolete; sometimes they are produced only on one side of the zooecium, sometimes on two. The buds themselves produce granddaughter and great-granddaughter buds, often connected together by short tubules, while still small and imperfectly developed. The swelling at the base of the zooecium, when the latter is fully formed, is small.

Polypide. The polypide has the features characteristic of the genus. The base of the gizzard is surrounded by a strong circular muscle.

A=single zooecium without adventitious buds but with a young resting bud (b), × 70 (dorsal view); B=lateral view of a smaller zooecium without buds, × 70; C=upper part of a zooecium with a single adventitious bud, × 70; D=outline of the upper part of a zooecium with adventitious buds of several generations, × 35; E=remains of a zooecium with two resting buds (b) attached. All the specimens figured are from Port Canning and, except D, are represented as they appear when stained with borax carmine and mounted in canada balsam.]

Resting buds. The resting buds (fig. 31, p. 170) are somewhat variable in shape but are always flat with irregular cylindrical or subcylindrical projections round the margin, on which the horny coat is thinner than it is on the upper surface. This surface is either smooth or longitudinally ridged.

TYPE in the Indian Museum.

This species differs from the European V. pavida in very much the same way as, but to a greater extent than, the Indian race of Bowerbankia caudata does from the typical English one (see p. 189). The growth of the zoarium is much more luxuriant, and the form of the resting buds is different.

GEOGRAPHICAL DISTRIBUTION.--V. bengalensis is abundant in pools of brackish water in the Ganges delta and in the Salt Lakes near Calcutta; it also occurs in ponds of fresh water near the latter. I have received specimens from Madras from Dr. J. R. Henderson, and it is probable that the form from Bombay referred by Carter to Paludicella belonged to this species.

BIOLOGY.--In the Ganges delta V. bengalensis is usually found coating the roots and stems of a species of grass that grows in and near brackish water, and on sticks that have fallen into the water. It also spreads over the surface of bricks, and I have found a specimen on a living shell of the common mollusc Melania tuberculata. Dr. Henderson obtained specimens at Madras from the surface of a freshwater shrimp, Palæmon malcolmsonii. In the ponds at Port Canning the zoaria grow side by side with, and even entangled with those of Bowerbankia caudata subsp. bengalensis, to the zooecia of which their zooecia bear a very strong external resemblance so far as their distal extremity is concerned. This resemblance, however, disappears in the case of zooecia that bear terminal buds, for no such buds are borne by B. caudata; and the yellowish tint of the zoaria of V. bengalensis is characteristic. Zoaria of the entoproct Loxosomatoides colonialis and colonies of the hydroid Irene ceylonensis are also found entangled with the zoaria of V. bengalensis, the zooecia of which are often covered with various species of Vorticellid protozoa and small rotifers. The growth of V. bengalensis is more vigorous than that of the other polyzoa found with it, and patches of B. caudata are frequently surrounded by large areas of V. bengalensis.

The food of V. bengalensis consists largely of diatoms, the siliceous shells of which often form the greater part of its excreta. Minute particles of silt are sometimes retained in the gizzard, being apparently swallowed by accident.

There are still many points to be elucidated as regards the production and development of the resting buds in V. bengalensis, but two facts are now quite clear as regards them: firstly, that these buds are produced at the approach of the hot weather and germinate in November or December; and secondly, that the whole zoarium may be transformed at the former season into a layer of resting buds closely pressed together but sometimes exhibiting in their arrangement the typical cruciform formation. Resting buds may often be found in vigorous colonies as late as the beginning of December; these buds have not been recently formed but have persisted since the previous spring and have not yet germinated. Sometimes only one or two buds are formed at the base of an existing zooecium (fig. 37 a), but apparently it is possible not only for a zooecium to be transformed into a resting bud but for it to produce four other buds round its base before undergoing the change. Young polypides are formed inside the buds and a single zooecium sprouts out of each, as a rule by the growth of one of the basal projections, when conditions are favourable.

Polypides of V. bengalensis are often transformed into brown bodies. When this occurs the orifice closes together, with the collar expanded outside the zooecium. I have occasionally noticed that the ectocyst of such zooecia was distinctly thicker and darker in colour than that of normal zooecia.

Eggs and spermatozoa are produced in great numbers, as a rule simultaneously in the same zooecia, but individuals kept in captivity often produce spermatozoa only. The eggs are small and are set free as eggs. Nothing is known as regards their development.

Polypides are as a rule found in an active condition only in the cold weather, but I have on one occasion seen them in this condition in August, in a small zoarium attached to a shell of Melania tuberculata taken in a canal of brackish water near Calcutta.

Family HISLOPIIDÆ.

HISLOPIDÉES, Jullien, Bull. Soc. zool. France, x, p. 180 (1885).

HISLOPIIDÆ, Annandale, Rec. Ind. Mus. i, p. 200 (1907).

Zoarium recumbent, often forming an almost uniform layer on solid subjects.

Zooecia flattened, adherent; the orifice dorsal, either surrounded by a chitinous rim or situated at the tip of an erect chitinous tubule; no parietal muscles.

Polypide with an ample gizzard which possesses a uniform chitinous lining and does not close together when the polypide is retracted.

Resting bud, not produced.

Only two genera can be recognized in this family, Arachnoidea, Moore, from Central Africa, and Hislopia, Carter, which is widely distributed in Eastern Asia. The former genus possesses an upright orificial tubule and has zooecia separated by basal tubules. Its anatomy is imperfectly known, but it certainly possesses a gizzard of similar structure to that of Hislopia, between which and Victorella its zooecium is intermediate in form.

Genus HISLOPIA, Carter.

Hislopia, Carter, Ann. Nat. Hist. (3) i, p. 169 (1858).

Hislopia, Stolickza, J. As. Soc. Bengal, xxxviii (2), p. 61 (1869).

Norodonia, Jullien, Bull. Soc. zool. France, v, p. 77 (1880).

Hislopia, id., ibid. x, p. 183 (1885).

Norodonia, id., ibid. p. 180.

Echinella, Korotneff, Biol. Centrbl. xxi, p. 311 (1901).

Hislopia, Annandale, J. As. Soc. Bengal (new series) ii, p. 59 (1906).

Hislopia, Loppens, Ann. Biol. lacustre, iii, p. 175 (1908).

TYPE, Hislopia lacustris, Carter.

Zoarium. The zoarium consists primarily of a main axis running in a straight line, with lateral branches that point forwards and outwards. Further proliferation, however, often compacts the structure into an almost uniform flat area.

Zooecia. The zooecia (fig. 35 B, p. 190) are flat and have the orifice surrounded by a chitinous rim but not much raised above the dorsal surface. They arise directly one from another.

Polypide. The polypide possesses from 12 to 20 tentacles. Its funiculus is rudimentary or absent. Neither the ovaries nor the testes have any fixed position on the lateral walls of the zooecium to which they are confined.

The position of this genus has been misunderstood by several zoologists. Carter originally described Hislopia as a cheilostome allied to Flustra; in 1880 Jullien perpetuated the error in describing his Norodonia, which was founded on dried specimens of Carter's genus; while Loppens in 1908 still regarded the two "genera" as distinct and placed them both among the cheilostomes. In 1885, however, Jullien retracted his statement that Norodonia was a cheilostome and placed it, together with Hislopia, in a family of which he recognized the latter as the eponymic genus. Carter's mistake arose from the fact that he had only examined preserved specimens, in which the thickened rim of the orifice is strongly reminiscent of the "peristome" of certain cheilostomes, while the posterior of the four folds into which the tentacle sheath naturally falls (as in all ctenostomes, cf. the diagram on p. 191) is in certain conditions rather larger than the other three and suggests the "lip" characteristic of the cheilostomes. If living specimens are examined, however, it is seen at once that the posterior fold, like the two lateral folds and the anterior one, changes its form and size from time to time and has no real resemblance to a "lip."

That there is a remarkable, if superficial, resemblance both as regards the form of the zooecium and as regards the method of growth between Hislopia and certain cheilostomes cannot be denied, but the structure of the orifice and indeed of the whole organism is that of a ctenostome and the resemblance must be regarded as an instance of convergence rather than of genetic relationship.

The most striking feature of the polypide of Hislopia is its gizzard (fig. 38, p. 201) which is perhaps unique (except for that of Arachnoidea) both in structure and function. In structure its peculiarities reside mainly in three particulars: (i), it is not constricted off directly from the thin-walled oesophageal tube, but possesses at its upper extremity a thick-walled tubular portion which can be entirely closed from the oesophagus at its upper end but always remains in communication with the spherical part of the gizzard; (ii), this spherical part of the gizzard is uniformly lined with a thick chitinous or horny layer which in optical section has the appearance of a pair of ridges; and (iii), there is a ring of long and very powerful cilia round the passage from the gizzard to the stomach. The cardiac limb of the stomach, which is large and heart-shaped, is obsolete. The wall of the spherical part of the gizzard consists of two layers of cells, an outer muscular layer consisting of powerful circular muscles and an inner glandular layer, which secretes the chitinous lining. The inner walls of the tubular part consist of non-ciliated columnar cells, and when the polypide is retracted it lies almost at right angles to the main axis of the zooecium.

The spherical part of the gizzard invariably contains a number of green cells, which lie free in the liquid it holds and are kept in motion by the cilia at its lower aperture. The majority of these cells can be seen with the aid of a high power of the microscope to consist of a hard spherical coat or cyst containing green protoplasm in which a spherical mass of denser substance (the nucleus) and a number of minute transparent granules can sometimes be detected. The external surface of many of the cysts is covered with similar granules, but some are quite clean.

There can be no doubt that these cysts represent a stage in the life-history of some minute unicellular plant or animal. Indeed, although it has not yet been found possible to work out this life-history in detail, I have been able to obtain much evidence that they are the resting stage of a flagellate organism allied to Euglena which is swallowed by the polyzoon and becomes encysted in its gizzard, extruding in so doing from its external surface a large proportion of the food-material that it has stored up within itself in the form of transparent granules. It may also be stated that some of the organisms die and disintegrate on being received into the gizzard, instead of encysting themselves.

So long as the gizzard retains its spherical form the green cells and its other contents are prevented from entering the stomach by the movements of the cilia that surround its lower aperture, but every now and then, at irregular intervals, the muscles that form its outer wall contract. The chitinous lining although resilient and not inflexible is too stiff to prevent the lumen of the gizzard being obliterated, but the action of the muscles changes its contents from a spherical to an ovoid form and in so doing presses a considerable part of them down into the stomach, through the ring of the cilia.

The contraction of the gizzard is momentary, and on its re-expansion some of the green cysts that have entered the stomach are often regurgitated into it. Some, however, remain in the stomach, in which they are turned round and round by the action of the cilia at both apertures. They are apparently able to retain their form for some hours in these circumstances but finally disintegrate and disappear, being doubtless digested by the juices poured out upon them by the glandular lining of the stomach. In polypides kept under observation in clean tap-water all the cysts finally disappear, and the fæces assume a green colour. In preserved specimens apparently unaltered cysts are sometimes found in the rectum, but this is exceptional: I have observed nothing of the kind in living polypides. Cysts often remain for several days unaltered in the gizzard.

Imperfect as these observations are, they throw considerable light on the functions of the gizzard in Hislopia. Primarily it appears to act as a food-reservoir in which the green cysts and other minute organisms can be kept until they are required for digestion. When in the gizzard certain organisms surrender a large proportion of the food-material stored up for their own uses, and this food-material doubtless aids in nourishing the polyzoon. Although the cysts in the gizzard are frequently accompanied by diatoms, the latter are not invariably present. The cysts, moreover, are to be found in the zooecia of polypides that have formed brown bodies, often being actually enclosed in the substance of the brown body. The gizzards of the specimens of Arachnoidea I have examined contain cysts that resemble those found in the same position in Hislopia.

Hislopia is widely distributed in the southern part of the Oriental Region, and, if I am right in regarding Echinella, Korotneff as a synonym, extends its range northwards to Lake Baikal. It appears to be a highly specialized form but is perhaps related, through Arachnoidea, to Victorella.

27. Hislopia lacustris, Carter.

Hislopia lacustris, Carter, Ann. Nat. Hist. (3) i, p. 170, pl. vii, figs. 1-3 (1858).

Norodonia cambodgiensis, Jullien, Bull. Soc. zool. France, v, p. 77, figs. 1-3 (1880).

Norodonia sinensis, id., ibid. p. 78, figs. 1-3.

Norodonia cambodgiensis, id., ibid. x, p. 181, figs. 244, 245 (1885).

Norodonia sinensis, id., ibid. p. 182, figs. 246, 247.

Hislopia lacustris, Annandale, J. As. Soc. Bengal (new series) iii, p. 85 (1907).

Hislopia lacustris, Walton, Rec. Ind. Mus. i, p. 177 (1907).

Hislopia lacustris, Kirkpatrick, ibid. ii, p. 98 (1908).

Hislopia lacustris, Walton, ibid. iii, p. 295 (1909).

Zoarium. The zoarium forms a flat, more or less solid layer and is closely adherent to foreign objects. As a rule it covers a considerable area, with radiating branches at the edges; but when growing on slender twigs or the stems of water-plants it forms narrow, closely compressed masses. One zooecium, however, never grows over another.

Zooecia. The zooecia are variable in shape. In zoaria which have space for free expansion they are as a rule irregularly oval, the posterior extremity being often narrower than the anterior; but small triangular zooecia and others that are almost square may often be found. When growing on a support of limited area the zooecia are smaller and as a rule more elongate. The orifice is situated on a slight eminence nearer the anterior than the posterior margin of the dorsal surface. It is surrounded by a strong chitinous rim, which is usually square or subquadrate but not infrequently circular or subcircular. Sometimes a prominent spine is borne at each corner of the rim, but these spines are often vestigial or absent; they are rarely as long as the transverse diameter of the orifice. The zooecium is usually surrounded by a chitinous margin, and outside this margin there is often a greater or less extent of adherent membrane. In some zooecia the margin is obsolete or obsolescent. The dorsal surface is of a glassy transparency but by no means soft.

A=part of a zoarium of the subspecies moniliformis (type specimen, from Calcutta), × 15; A=green cysts in gizzard; E=eggs.

B=outline of part of a zoarium of the typical form of the species from the United Provinces, showing variation in the form of the zooecia and of the orifice, × 15.]

Polypide. The polypide has from 12 to 20 tentacles, 16 being a common number.

TYPE probably not in existence. It is not in the British Museum and Prof. Dendy, who has been kind enough to examine the specimens from Carter's collection now in his possession, tells me that there are none of Hislopia among them.

27 a. Subsp. moniliformis, nov.

Hislopia lacustris, Annandale, J. As. Soc. Bengal (new series) ii, p. 59, fig. 1 (1906).

In this race, which is common in Calcutta, the zooecia are almost circular but truncate or concave anteriorly and posteriorly. They form linear series with few lateral branches. I have found specimens occasionally on the shell of Vivipara bengalensis, but they are much more common on the leaves of Vallisneria spiralis.

TYPE in the Indian Museum.

The exact status of the forms described by Jullien as Norodonia cambodgiensis and N. sinensis is doubtful, but I see no reason to regard them as specifically distinct from H. lacustris, Carter, of which they may be provisionally regarded as varieties. The variety cambodgiensis is very like my subspecies moniliformis but has the zooecia constricted posteriorly, while var. sinensis, although the types were found on Anodonta shells on which there was plenty of room for growth, resemble the confined phase of H. lacustris so far as the form of their zooecia and of the orifice is concerned.

GEOGRAPHICAL DISTRIBUTION.--The typical form is common in northern India and occurs also in Lower Burma; the subspecies moniliformis appears to be confined to Lower Bengal, while the varieties cambodgiensis and sinensis both occur in China, the former having been found also in Cambodia and Siam. Indian and Burmese localities are:--BENGAL, Calcutta (subsp. moniliformis); Berhampur, Murshidabad district (J. Robertson Milne): CENTRAL PROVINCES, Nagpur (Carter): UNITED PROVINCES, Bulandshahr (H. J. Walton): BURMA, Pegu-Sittang Canal (Kirkpatrick).

BIOLOGY.--Regarding the typical form of the species Major Walton writes (Rec. Ind. Mus. iii, p. 296):--"In volume i (page 177) of the Records of the Indian Museum, I described the two forms of colonies of Hislopia that I had found in the United Provinces (Bulandshahr). Of these, one was a more or less linear arrangement of the zooecia on leaves and twigs, and the other, and more common, form was an encrusting sheath on the outer surface of the shells of Paludina. During the present 'rains' (July 1908) I have found many examples of what may be considered a much exaggerated extension of the latter form. These colonies have been on bricks, tiles, and other submerged objects. The largest colony that I have seen so far was on a tile; one side of the tile was exposed above the mud of the bottom of the tank, and its area measured about 120 square inches; the entire surface was almost completely covered by a continuous growth of Hislopia. Another large colony was on a piece of bark which measured 7 inches by 3 inches; both sides were practically everywhere covered by Hislopia."

Major Walton also notes that in the United Provinces the growth of Hislopia is at its maximum during "rains," and that at that time of year almost every adult Paludina in a certain tank at Bulandshahr had its shell covered with the zooecia. The Calcutta race flourishes all the year round but never forms large or closely compacted zoaria, those on shells of Vivipara exactly resembling those on leaves of Vallisneria.

In Calcutta both eggs and spermatozoa are produced at all times of the year simultaneously in the same zooecia, but the eggs in one zooecium often vary greatly in size. When mature they reach relatively considerable dimensions and contain a large amount of food material; but they are set free from the zooecium as eggs. They lie loose in the zooecium at a comparatively small size and grow in this position. Nothing is known as regards the development of Hislopia.

Both forms of the species appear to be confined to water that is free from all traces of contamination with brine.

Order PHYLACTOLÆMATA.

The polypide in this order possesses a leaf-like ciliated organ (the epistome) which arises within the lophophore between the mouth and the anus and projects upwards and forwards over the mouth, which it can be used to close. The zooecia are never distinct from one another, but in dendritic forms such as Plumatella the zoarium is divided at irregular intervals by chitinous partitions. The lophophore in most genera is horseshoe-shaped instead of circular, the part opposite the anus being deeply indented. There are no parietal muscles. The orifice of the zooecium is always circular, and there is no trace of any structure corresponding to the collar of the ctenostomes. The tentacles are always webbed at the base.

All the phylactolæmata produce the peculiar reproductive bodies known as statoblasts.

The phylactolæmata, which are probably descended from ctenostomatous ancestors, are confined to fresh or slightly brackish water. Most of the genera have a wide geographical distribution, but (with the exception of a few statoblasts of almost recent date) only one fossil form (Plumatellites, Fric. from the chalk of Bohemia) has been referred to the order, and that with some doubt.

It is convenient to recognize two main divisions of the phylactolæmata, but these divisions hardly merit the distinction of being regarded as suborders. They may be called Cristatellina and Plumatellina and distinguished as follows:--

Division I, PLUMATELLINA, nov.--Ectocyst well developed; zoaria without a special organ of progression; polypides contained in tubes.

Division II, CRISTATELLINA, nov.--Ectocyst absent except at the base of the zoarium which is modified to form a creeping "sole"; polypides embedded in a common synoecium of reticulate structure.

The Cristatellina consist of a single genus and probably of a single species (Cristatella mucedo, Cuvier), which is widely distributed in Europe and N. America, but has not been found in the Oriental Region. Eight genera of Plumatellina are known, and five (possibly six) of these genera occur in India.

Division PLUMATELLINA, nov.

The structure of the species included in this division is very uniform as regards the internal organs (see fig. 40 opposite and fig. 47 a, p. 236). The alimentary canal is simpler than that of the Paludicellidæ. A short oesophagus leads directly into the stomach, the cardiac portion of which is produced as a vertical limb almost cylindrical in form and not constricted at the base. This limb is as a rule of greater length than the oesophagus. The pyloric part of the stomach is elongated and narrow, and the intestine short, straight, and of ovoid form. There are no cilia at the pyloric opening. A single funiculus joins the posterior end of the stomach to the wall of the zooecium, bearing the statoblasts. Sexual organs are often absent.

A=a zooecium of Fredericella with the polypide extruded. B=the lophophore of Lophopus (tentacles removed) as seen obliquely from the right side. C=larva of Plumatella as seen in optical section. a=tentacles; b=velum; c=epistome; d=mouth; e=oesophagus; f=stomach; g=intestine; h=anus; j=retractor muscle; k=parieto-vaginal muscles; l=funiculus.]

Two families may be recognized as constituting the division, viz., (a) the Fredericellidæ, which have a circular or oval lophophore and simple statoblast without a swim-ring, and (b) the Plumatellidæ, in which the lophophore is shaped like a horseshoe and some or all of the statoblasts are provided with a ring of air-spaces.

Family 1. FREDERICELLIDÆ.

FREDERICELLIDÆ, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 168 (1887).

Zoaria dendritic; zooecia distinctly tubular, with the ectocyst well developed; statoblasts of one kind only, each surrounded by a chitinous ring devoid of air-spaces; polypides with the lophophore circular or oval when expanded.

The Fredericellidæ consist of a single genus (Fredericella) which includes several closely-allied forms and has a wide geographical distribution.

Genus FREDERICELLA, Gervais (1838).

Fredericella, Allman, Mon. Fresh-Water Polyzoa, p. 11 (1857).

Plumatella, ("arrêt de développement") Jullien, Bull. Soc. zool. France, x, p. 121 (1885).

Fredericella, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 99 (1887).

Fredericella, Goddard, Proc. Linn. Soc. N. S. Wales, xxxiv, p. 489 (1909).

This genus has the characters of the family. Its status has been much disputed, some authors regarding the shape of the lophophore as of great morphological importance, while Jullien believed that Fredericella was merely an abnormal or monstrous form of Plumatella. The latter belief was doubtless due to the fact that the zoaria of the two genera bear a very close external resemblance to one another and are sometimes found entangled together. The importance of the shape of the lophophore may, however, easily be exaggerated, for, as both Jullien and Goddard have pointed out, it assumes an emarginate form when retracted.

The best known species is the European and N. American F. sultana (Blumenbach), of which several varieties or phases have been described as distinct. This form is stated to occur also in S. Africa. F. australiensis, Goddard from N. S. Wales is said to differ from this species in having an oval instead of a circular lophophore and in other small anatomical characters; but it is doubtful how far these characters are valid, for the lophophore appears to be capable of changing its shape to some slight extent and has been stated by Jullien to be habitually oval in specimens from France. F. cunningtoni, Rousselet from Lake Tanganyika has stout zooecia encrusted with relatively large sand-grains.

The zoaria of Fredericella are usually found attached to solid objects in shallow water, but a form described as F. duplessisi, Ford has been found at a depth of 40 fathoms embedded in mud at the bottom of the Lake of Geneva. F. cunningtoni was dredged from depths of about 10 and about 25 fathoms.

The statoblasts of this genus do not float and often germinate in the parent zooecium after its polypides have died. They are produced in smaller numbers than is usually the case in other genera of the order. The polypides sometimes undergo a process of regeneration, but without the formation of brown bodies.

A=statoblast, × 120. B=outline of expanded lophophore and adjacent parts, × 75; a=anus, r=rectum. C=outline of zoarium on leaf of water-plant, × 3.

(A and B are from specimens from Igatpuri, C from specimen from Shasthancottah).]

28. Fredericella indica, Annandale.

Fredericella indica, Annandale, Rec. Ind. Mus. iii, p. 373, fig. (1909).

Fredericella indica, id., ibid. v, p. 39 (1910).

Zoarium. The zoarium is of delicate appearance and branches sparingly. It is often entirely recumbent but sometimes produces short, lax branches that consist of two or three zooecia only.

Zooecia. The zooecia are very slender and almost cylindrical; they are slightly emarginate and furrowed, the keel in which the furrow runs being sometimes prominent. The external surface is minutely roughened and apparently soft, for small grains of sand and other débris cling to it, but never thickly. The ectocyst is practically colourless but not transparent.

Statoblasts. The statoblasts are variable in size and form but most commonly have a regular broad oval outline; sometimes they are kidney-shaped. The dorsal surface is covered with minute star-shaped prominences, which sometimes cover it almost uniformly and are sometimes more numerous in the centre than towards the periphery. The ventral surface is smooth.

Polypide. The lophophore bears about 20-25 tentacles, which are very slender and of moderate length; the velum at their base is narrow; as a rule the lophophore is accurately circular.

TYPE in the Indian Museum.

The most definite character in which this species differs from F. sultana and F. australiensis is the ornamentation of one surface of the statoblast, both surfaces of which are smooth in the two latter species. From F. cunningtoni, the statoblasts of which are unknown, it differs in having almost cylindrical instead of depressed zooecia and in not having the zooecia densely covered with sand-grains.

GEOGRAPHICAL DISTRIBUTION.--Western India (the Malabar Zone): Igatpuri Lake, W. Ghats (alt. ca. 2,000 feet), Bombay Presidency, and Shasthancottah Lake near Quilon, Travancore.

BIOLOGY.--In both the lakes in which the species has yet been found it was collected in November. The specimens obtained in Travancore were found to be undergoing a process of regeneration due at least partly to the fact that most of the polypides had perished and that statoblasts were germinating in the old zooecia. Specimens from the Bombay Presidency, which were obtained a little later in the month, were in a more vigorous condition, although even they contained many young polypides that were not yet fully formed. It seems, therefore, not improbable that F. indica dies down at the beginning of the hot weather and is regenerated by the germination of its statoblasts at the beginning of the cold weather.

At Shasthancottah zoaria were found entangled with zoaria of a delicate form of Plumatella fruticosa to which they bore a very close external resemblance.

Family 2. PLUMATELLIDÆ.

PLUMATELLIDÆ, Allman (partim), Mon. Fresh-Water Polyzoa, pp. 76, 81 (1857).

Phylactolæmata which have horseshoe-shaped lophophores and a well-developed ectocyst not specialized to form an organ of progression. Some or all of the statoblasts are provided with a "swim-ring" consisting of symmetrically disposed, polygonal chitinous chambers containing air.

It is convenient to divide the Plumatellidæ as thus defined into subfamilies (the Plumatellinæ and the Lophopinæ), which may be defined as follows:--

Subfamily A. PLUMATELLINÆ.

Zoarium dendritic or linear, firmly fixed to extraneous objects; zooecia tubular, not fused together to form a gelatinous mass.

Subfamily B. LOPHOPINÆ.

Zoarium forming a gelatinous mass in which the tubular nature of the zooecia almost disappears, capable to a limited extent of progression along a smooth surface.

Both these subfamilies are represented in the Indian fauna, the Plumatellinæ by two of the three genera known to exist, and the Lophopinæ by two (or possibly three) of the four that have been described. The following key includes all the known genera, but the names of those that have not been recorded from India are enclosed in square brackets.

Key to the Genera of Plumatellidæ.

I. Statoblasts without marginal processes. A. Zooecia cylindrical, not embedded in a gelatinous investment (Plumatellinæ). a. Zooecia arising directly from one another; no stolon; free statoblast oval PLUMATELLA, p. 212. a'. Zooecia arising singly or in groups from an adherent stolon; free statoblasts oval. STOLELLA, p. 229. B. Zooecia cylindrical, embedded in a structureless gelatinous investment. Zooecia arising from a ramifying stolon; statoblasts circular [STEPHANELLA.] C. Polypides embedded in a hyaline synoecium that conceals the cylindrical form of the zooecia (Lophopinæ). c. Polypides upright, their base far removed from that of the zoarium when they are expanded LOPHOPUS, p. 231. c'. Polypides recumbent for the greater part of their length at the base of the zoarium [AUSTRALELLA.] II. Statoblasts armed (normally) with hooked processes (Lophopinæ). A. Processes confined to the extremities of the statoblast; zoaria remaining separate throughout life LOPHOPODELLA, p. 231. B. Processes entirely surrounding the statoblast; many zoaria embedded in a common gelatinous investment so as to form large compound colonies PECTINATELLA, p. 235.

Subfamily A. PLUMATELLINÆ.

Of the two Indian genera of this subfamily, one (Plumatella) is almost universally distributed, while the other (Stolella) has only been found in the valley of the Ganges. The third genus of the subfamily (Stephanella) is only known from Japan.

It should be noted that zoaria of different species and genera of this subfamily are often found in close proximity to one another and to zoaria of Fredericella, and that the branches of the different species are sometimes entangled together in such a way that they appear, unless carefully separated, to belong to the same zoarium.

Genus 1. PLUMATELLA, Lamarck.

Plumatella, Lamarck, Animaux sans Vert. (ed. 1re) ii, p. 106 (1816).

Alcyonella, id., ibid. p. 100.

Plumatella, Allman, Mon. Fresh-Water Polyzoa, p. 92 (1857).

Alcyonella, id., ibid. p. 86.

Plumatella, Hyatt, Comm. Essex Inst. iv, p. 207, pl. viii (1866).

Plumatella, Jullien (partim), Bull. Soc. zool. France, x, p. 100 (1885).

Hyalinella, id., ibid. p. 133.

Plumatella, Kraepelin, Deutsch. Süsswass. Bryozoen, i, p. 104 (1887).

Plumatella, Braem, Unter. ü. Bryozoen des süssen Wassers, p. 2 (Bibliotheca Zoologica, ii, 1890).

Zoarium dendritic, recumbent, erect, or partly recumbent and partly erect.

Zooecia tubular, not confined in a gelatinous synoecium; the ectocyst usually horny.

Statoblasts often of two kinds, free and stationary, the latter without air-cells and as a rule adherent by one surface, the former provided with a well-developed ring of air-cells but without marginal processes, oval in form, never more than about 0.6 mm. in length.

Polypide with less than 65 tentacles.

A, of P. fruticosa (Calcutta); B, of P. emarginata (Calcutta); C, of P. javanica (Travancore); D, of P. diffusa (Sikhim); E, of P. allmani (Bhim Tal); F, of P. diffusa (Rajshahi, Bengal); G, G', of P. punctata (Calcutta); H, of P. diffusa (Sikhim), statoblast further enlarged: A=outline of capsule; B=limit of swim-ring on ventral surface; C=limit of swim-ring on dorsal surface. [The dark area represents the capsule of the statoblast.]]

Certain forms of this genus are liable to become compacted together in such a way as to constitute solid masses consisting of elongate vertical zooecia closely parallel to one another and sometimes agglutinated by means of a gummy substance. These forms were given by Lamarck in 1816 the name Alcyonella, and there has been much dispute as to whether they represent a distinct genus, distinct species, or merely varieties or phases of more typical forms. It appears to be the case that all species which produce vertical branches are liable to have these branches closely packed together and the individual zooecia of which they are composed more or less greatly elongated. It is in this way that the form known to Allman as Alcyonella benedeni is produced from the typical Plumatella emarginata. Other forms go further and secrete a gummy substance that glues the upright zooecia together and forces them to elongate themselves without branching. In these conditions the zooecia become polygonal in cross-section. It is probable that such forms (e. g., Plumatella fungosa (Pallas)) should rank as distinct species, for the gummy secretion is present in great profusion even in young zoaria in which the zooecia have not yet assumed a vertical position. No such form, however, has as yet been found in India, and in any case it is impossible to regard Alcyonella as a distinct genus.

Key to the Indian Species of Plumatella.

I. Ectocyst more or less stiff, capable of transverse wrinkling only near the tips of the zooecia, never contractile or greatly swollen; zooecia rounded at the tip when the polypide is retracted. Free statoblasts elongate; the free portion of their swim-ring distinctly narrower at the sides than at the ends. A. Ectocyst by no means rigid, of a uniform pale colour; zooecia never emarginate or furrowed, straight, curved or sinuous, elongate, cylindrical fruticosa, p. 217. B. Ectocyst rigid; zooecia (or at any rate some of the zooecia) emarginate and furrowed. b. Ectocyst darkly pigmented over the greater part of each zooecium, white at the tip; branching of the zoarium practically dichotomous, profuse, as a rule both horizontal and vertical; zooecia straight or slightly curved or sinuous emarginata, p. 220. b'. Ectocyst colourless and hyaline; branching of the zoarium sparse, lateral, irregular, horizontal; zooecia nearly straight, strongly emarginate and furrowed javanica, p. 221. b''. The majority of the zooecia distinctly L-shaped, one limb being as a rule adherent; ectocyst never densely pigmented. beta. Zooecia cylindrical, their furrowed keel never prominent diffusa, p. 223. beta'. Zooecia (or at any rate some of the zooecia) constricted or tapering at the base, their emargination and furrow conspicuous allmani, p. 224.

II. Ectocyst stiff; zooecia truncated when the polypide is retracted. Surface of zooecia minutely roughened, distinctly annulate on the distal part tanganyikæ, p. 225. III. Ectocyst swollen and contractile, capable of transverse wrinkling all over the zooecium; zooecia never emarginate punctata, p. 227.

There has always been much difficulty in separating the species of Plumatella, and even now there is no general consensus of opinion as to the number that should be recognized. The difficulty, however, is much reduced if the following precautions are observed:--

(1) If the zoarium appears to be tangled, if the branches intertwine or overlap, or if the zooecia are closely pressed together, the whole mass should be carefully dissected out. This is necessary not only because zoaria belonging to different species are sometimes found entangled together but also because it is often difficult to recognize the characteristic method of branching and shape of the zooecia unless it is done.

(2) As large a part as possible of each zoarium should be examined, preferably with a binocular microscope, and allowance should be made for irregularities and abnormalities of all kinds. What must be observed is the rule rather than the exceptions.

(3) When the statoblasts are being examined, care must be taken that they lie flat and that their surface is parallel to that of the nose-piece of the microscope. If they are viewed obliquely it is impossible to see their true outlines and proportions.

(4) In order to see the relative proportions of the capsule and the swim-ring it is necessary that the statoblast should be rendered transparent. This is often difficult owing to the presence of air in the air-cells, but strong nitric acid applied judiciously will render it possible (p. 240).

In supervising the preparation of the plates that illustrate this genus I have impressed upon the artist the importance of representing what he saw rather than what he thought he ought to see, and the figures are very close copies of actual specimens. I have deliberately chosen for representation specimens of Plumatella preserved by the simple methods which are often the only ones that it is possible for a traveller to adopt, for the great majority of naturalists will probably have no opportunity of examining living specimens or specimens preserved by special methods, and the main object, I take it, of this series is to enable naturalists first to distinguish the species described and then to learn something of their habitat and habits.

GEOGRAPHICAL DISTRIBUTION.--Of the seven species included in this key five have been found in Europe (namely P. fruticosa, P. emarginata, P. diffusa, P. allmani, and P. punctata), while of these five all but P. allmani are known to occur in N. America also. P. javanica is apparently peculiar to the Oriental Region, while P. tanganyikæ has only been taken in Central Africa and in the Bombay Presidency.

TYPES.--Very few of the type-specimens of the older species of Plumatella are in existence. Allman's are neither in Edinburgh nor in London, and Mr. E. Leonard Gill, who has been kind enough to go through the Hancock Collection at Newcastle-on-Tyne, tells me that he cannot trace Hancock's. Those of the forms described by Kraepelin are in Hamburg and that of P. tanganyikæ in the British Museum, and there are schizotypes or paratypes of this species and of P. javanica in Calcutta. The types of Leidy's species were at one time in the collection of the Philadelphia Academy of Science.

BIOLOGY.--The zoaria of the species of Plumatella are found firmly attached to stones, bricks, logs of wood, sticks, floating seeds, the stems and roots of water-plants, and occasionally to the shells of molluscs such as Vivipara and Unio. Some species shun the light, but all are apparently confined to shallow water.

Various small oligochæte worms (e. g., Chætogaster spongillæ, Nais obtusa, Nais elinguis, Slavina appendiculata and Pristina longiseta), take shelter amongst them; dipterous larvæ of the genus Chironomus often build their protective tubes at the base of the zoaria, and the surface of the zooecia commonly bears a more or less profuse growth of such protozoa as Vorticella and Epistylis. I have seen a worm of the genus Chætogaster devouring the tentacles of a polypide that had been accidentally injured, but as a rule the movements of the lophophore are too quick to permit attacks of the kind, and I know of no active enemy of the genus. The growth of sponges at the base of the zoaria probably chokes some species, but one form (F. fruticosa) is able to surmount this difficulty by elongating its zooecia (p. 219). A small worm (Aulophorus tonkinensis) which is common in ponds in Burma and the east of India as far west as Lucknow, often builds the tube in which it lives mainly of the free statoblasts of this genus. It apparently makes no selection in so doing but merely gathers the commonest and lightest objects it can find, for small seeds and minute fragments of wood as well as sponge gemmules and statoblasts of other genera are also collected by it. I know of no better way of obtaining a general idea as to what sponges and phylactolæmata are present in a pond than to examine the tubes of Aulophorus tonkinensis.

I am indebted to Mr. F. H. Gravely, Assistant Superintendent in the Indian Museum, for an interesting note regarding the food of Plumatella. His observations, which were made in Northamptonshire, were unfortunately interrupted at a critical moment, but I have reproduced them with his consent in order that other observers may investigate the phenomena he saw. Mr. Gravely noted that a small green flagellate which was abundant in water in which Plumatella repens was growing luxuriantly, was swallowed by the polypides, and that if the polyparium was kept in a shallow dish of water, living flagellata of the same species congregated in a little pile under the anus of each polypide. His preparations show very clearly that the flagellates were passing through the alimentary canal without apparent change, but the method of preservation does not permit the retractile granules, which were present in large numbers in the cell-substance of the flagellates, to be displayed and it is possible that these granules had disappeared from those flagellates which are present in the recta of his specimens. It is clear, therefore, either that certain flagellates must pass through the alimentary canal of Plumatella unchanged, or that the polyzoon must have the power of absorbing the stored food material the flagellates contain without doing them any other injury.

The free statoblasts of Plumatella are as a rule set free before the cells they contain become differentiated, and float on the surface of the water for some time before they germinate; but occasionally a small polypide is formed inside the capsule while it is still in its parent zooecium. I have, however, seen only one instance of this premature development, in a single statoblast contained in a small zoarium of P. fruticosa found in Lower Burma in March. The fixed statoblasts usually remain fixed to the support of the zoarium, even when their parent-zooecium decays, and germinate in situ.

The larva (fig. 40 C, p. 207) that originates from the egg of Plumatella is a minute pear-shaped, bladder-like body covered externally with fine vibratile threads (cilia) and having a pore at the narrow end. At the period at which it is set free from the parent zooecium it already contains a fully formed polypide or pair of polypides with the tentacles directed towards the narrow end. After a brief period of active life, during which it moves through the water by means of its cilia, it settles down on its broad end, which becomes adhesive; the polypide or pair of polypides is everted through the pore at the narrow end, the whole of this end is turned inside out, and a fresh polyparium is rapidly formed by budding.

29. Plumatella fruticosa, Allman. (Plate III, fig. 1; plate IV, fig. 4; plate V, fig. 1.)

Plumatella fruticosa, Allman, Ann. Nat. Hist. xiii, p. 331 (1844).

Plumatella repens, van Beneden (? nec Linné), Mém. Acad. Roy. Belg. 1847, p. 21, pl. i, figs. 1-4.

Plumatella fruticosa, Johnston, Brit. Zooph. (ed. 2), p. 404 (1847).

Plumatella coralloides, Allman, Rep. Brit. Assoc. 1850, p. 335.

Plumatella stricta, id., Mon. Fresh-Water Polyzoa, p. 99, fig. 14 (1857).

Plumatella fruticosa, id., ibid. p. 102, pl. vi, figs. 3-5.

Plumatella coralloides, id., ibid. p. 103, pl. vii, figs. 1-4.

Plumatella repens and P. stricta, Carter, Ann. Nat. Hist. (3) iii, p. 341 (1859).

Plumatella lucifuga, Jullien (partim), Bull. Soc. zool. France, x, p. 114 (1885).

Plumatella princeps var. fruticosa, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 120, pl. vii, fig. 148 (1887).

Plumatella fruticosa, Braem, Unter. ii. Bryozoen des süssen Wassers, p. 9, pl. i, fig. 15 (Bibl. Zool. ii) (1890).

Plumatella repens, Annandale, J. As. Soc. Bengal (new series) iii, 1907, p. 88.

Plumatella emarginata, Loppens (partim), Ann. Biol. lacustre, iii, p. 161 (1908).

Plumatella fruticosa, Annandale, Rec. Ind. Mus. v, p. 45 (1910).

Zoarium. The zoarium in the typical form has a loose appearance due to the fact that the branches are far apart and the ectocyst by no means rigid. When young the zoarium is adherent, but in well-grown polyparia vertical branches, often an inch or more in length, are freely produced. As a rule they have not the strength to stand upright if removed from the water. Branching is ordinarily lateral and as a rule occurs chiefly on one side of a main branch or trunk. In certain circumstances upright zooecia are pressed together and reach a great length without branching, and in this form (P. coralloides, Allman) daughter-zooecia are often produced at the tip of an elongated mother-zooecium in fan-like formation. A depauperated form (P. stricta, Allman), occurs in which the vertical branches are absent or very short. In all forms internal partitions are numerous and stout.

Zooecia. The zooecia are cylindrical and bear a simple keel on their dorsal surface. They are never emarginate or furrowed. In the typical form their diameter is more than half a millimetre, and they are always of considerable length. The ectocyst is thin and never very rigid or deeply pigmented, the colour usually being an almost uniform pale pinkish brown and fading little towards the tip of the zooecium.

Statoblasts. Both free and stationary statoblasts are formed, but the latter are rare and do not always adhere. They resemble the free statoblasts in general form but have a solid margin instead of a swim-ring and are often minutely serrated round the edge. The free statoblasts are at least considerably, sometimes very elongate; in all zoaria it is possible to find specimens that are more than twice as long as broad. The capsule is relatively large and resembles the swim-ring in outline, so that the free portion of the latter is not much narrower at the sides than at the ends. The sides are distinctly convex and the ends rounded; the swim-ring encroaches little on the surface of the capsule.

Polypide. The tentacles number between 40 and 50 and are not festooned at the base. The stomach is slender and elongate.

TYPE not in existence.

SYSTEMATIC REMARKS.--P. fruticosa is closely allied to P. repens (European and N. American) but always has much longer statoblasts. Three phases of the species may be distinguished as follows:--

A. (Forma typica). Zooecia stout in form, not greatly elongate; free branches produced in profusion.

B. (P. stricta, Allman, P. repens, van Beneden). Zooecia slender; free branches absent or consisting of two or three zooecia only.

C. (P. coralloides, Allman). Vertical zooecia pressed together and greatly elongated.

Indian specimens of the typical form agree well with German specimens labelled by Prof. Kraepelin P. princeps var. fruticosa, and specimens of the coralloides phase could hardly be distinguished from similar specimens from Scotland.

GEOGRAPHICAL DISTRIBUTION.--P. fruticosa is widely distributed in Europe and probably in N. America. I have seen Indian specimens from the Punjab (Lahore, Stephenson), from Bombay, from Travancore, from Calcutta and other places in the Ganges delta, from Rajshahi (Rampur Bhoolia) on the R. Ganges, from Kurseong in the E. Himalayas (alt. 4,500 feet), and from Kawkareik in Tenasserim. Statoblasts found on the surface of a pond near Simla in the W. Himalayas (alt. ca. 8,000 feet), probably belong to this species.

BIOLOGY.--Allman states that in England P. fruticosa is fond of still and slowly-running water. The typical form and the coralloides phase grow abundantly in the Calcutta tanks, the former often attaining an extraordinary luxuriance. I have found the var. stricta only in water in which there was reason to suspect a lack of minute life (and therefore of food), viz. in Shasthancottah Lake in Travancore, in a swamp in Lower Burma, and in a small jungle stream near the base of the Western Ghats in Travancore. The species is the only one that I have seen in running water in India, and the specimens obtained in the jungle stream in Travancore are the only specimens I have taken in these circumstances. P. fruticosa always grows near the surface or near the edge of water; it is found attached to the stems of bulrushes and other aquatic plants, to floating seeds and logs and (rarely) to stones and bricks. So far as my experience goes it is only found, at any rate in Calcutta, in the cold weather and does not make its appearance earlier than October.

The form Allman called P. coralloides was found by him, "attached to floating logs of wood, together with P. repens and Cordylophora lacustris, and generally immersed in masses of Spongilla fluviatilis." I have always found it immersed in sponges (S. lacustris, S. alba, S. carteri, and S. crassissima), except when the sponge in which it had been immersed had decayed. Indeed, the peculiar form it has assumed appears to be directly due to the pressure of the growing sponge exerted on the zooecia, for it is often possible to find a zoarium that has been partially overgrown by a sponge and has retained its typical form so long as it was free but has assumed the coralloides form where immersed. In Shasthancottah Lake, Travancore, I found specimens of the stricta phase embedded in the gelatinous mass formed by a social rotifer and to some extent assimilated to the coralloides form.

30. Plumatella emarginata, Allman. (Plate III, fig. 2; plate IV, figs. 1, 1 a.)

Plumatella emarginata, Allman, Ann. Nat. Hist. xiii, p. 330 (1844).

Plumatella emarginata, Johnston, Brit. Zooph. (ed. 2), p. 404 (1847).

Alcyonella benedeni, Allman, Mon. Fresh-Water Polyzoa, p. 89, pl. iv, figs. 5-11 (1857).

Plumatella emarginata, id., ibid. p. 104, pl. vii, figs. 5-10.

Plumatella lucifuga, Jullien, Bull. Soc. zool. France, x, figs. 89, 90, p. 114 (1885).

Plumatella princeps var. emarginata, Kraepelin (partim), Deutsch. Süsswasserbryoz. p. 120, pl. iv, fig. 108, pl. v, fig. 123 (1887).

Plumatella emarginata, Braem, Unter. ii. Bryoz. süssen Wassers, p. 9, pl. i, figs. 12, 14 (Bibl. Zool. ii) (1890).

Plumatella emarginata, Annandale (partim), J. As. Soc. Bengal, (new series) iii, 1907, p. 89.

Plumatella princeps, Loppens (partim), Ann. Biol. lacustre, iii, p. 162, fig. 7 (1908).

Plumatella emarginata, Annandale, Rec. Ind. Mus. v, p. 47 (1910).

Zoarium. The zoarium often covers a considerable area on flat surfaces and is sometimes entirely recumbent. More usually, however, the younger part is vertical. In either case the branching is practically dichotomous, two young zooecia arising almost simultaneously at the tip of a mother-zooecium and diverging from one another at a small angle. When the zoarium becomes vertical, rigid branches of as much as an inch in length are sometimes produced in this way and, arising parallel to one another, are pressed together to form an almost solid mass (=Alcyonella benedeni, Allman). In such cases the basal zooecium or at any rate the basal part of each upright branch is considerably elongated. In recumbent zooecia the main branches often radiate outwards from a common centre.

Zooecia. The zooecia are of almost equal width throughout, slender, and moderately elongate when recumbent. Their ectocyst is stiff; they are emarginate at the tip and more or less distinctly furrowed on the dorsal surface, the keel in which the furrow runs not being prominent. The orifice is often on the dorsal surface even in upright branches. Each zooecium is of a dark brown or almost black colour for the greater part of its length but has a conspicuous white tip which is extended down the dorsal surface in the form of a triangle, its limits being rather more extensive than and parallel to those of the emargination.

Statoblast. The majority of the free statoblasts are elongate and truncate or subtruncate at the extremities, the sides being as a rule straight and parallel. In every polyparium specimens will be found that are between twice and thrice as long as broad. The capsule is, however, relatively much broader than the swim-ring, often being nearly circular, and there is therefore at either end a considerable extent of free air-cells, while the extent of these cells at the sides of the capsule is small. The air-cells cover a considerable part of the dorsal surface of the capsule. Fixed statoblasts are usually found in old colonies, especially at the approach of the hot weather. They have an oval form and are surrounded by a membranous margin on which traces of reticulation can often be detected. As a rule statoblasts of both types are produced in considerable but not in excessive numbers.

Polypide. There are about 40 tentacles, the velum at the base of which extends upwards for a considerable distance without being festooned. The stomach is elongate and slender and narrowly rounded at the base.

The method of branching, the coloration of the zooecia and the form of the free statoblast are all characteristic. Luxuriant or closely compressed zoaria of P. diffusa often bear a superficial resemblance to those of P. emarginata, but the resemblance disappears if they are carefully dissected out. Indian specimens of P. emarginata agree closely with European ones.

GEOGRAPHICAL DISTRIBUTION.--P. emarginata is a common species in Europe, N. America, and southern Asia and probably also occurs in Africa and Australia. I have examined specimens from Calcutta, Rangoon, and Mandalay in Indian territory, and also from Jalor in the Patani States (Malay Peninsula) and the Talé Noi, Lakon Sitamarat, Lower Siam. Gemmules found by Apstein (Zool. Jahrb. (Syst.) xxv, 1907, p. 201) in plankton from the Colombo lake may belong to this species or to any of the others included by Kraepelin in his P. princeps.

BIOLOGY.--In Ireland Allan found P. emarginata in streams and rivulets, but it also occurs in European lakes. In India I have only found it in ponds. It prefers to adhere to the surface of stones or bricks, but when these are not available is found on the stems of water-plants. In the latter position the form called Alcyonella benedeni by Allman is usually produced, owing to the fact that the upright branches are crowded together through lack of space, very much in the same way (although owing to a different cause) as those of P. fruticosa are crowded together in the coralloides phase, to which the benedeni phase of P. emarginata is in many respects analogous.

Although it is essentially a cold-weather species in Calcutta, P. emarginata is sometimes found in a living condition during the "rains." Zoaria examined at this season, however, contains few living polypides, the majority of the zooecia having rotted away and left fixed statoblasts only to mark their former position.

31. Plumatella javanica, Kraepelin.

Plumatella javanica, Kraepelin, Mitt. Nat. Mus. Hamb. xxiii, p. 143, figs. 1-3 (1903).

Plumatella emarginata var. javanica, Loppens, Ann. Biol. lacustre, iii, p. 162 (1908).

Plumatella javanica, Annandale, Rec. Ind. Mus. v, p. 50 (1910).

Plumatella allmani var. dumortieri, id. (partim) (nec Allman), ibid. p. 49.

This species is related to P. emarginata, from which it may be distinguished by the following characters:--

Zoarium. The zoarium is always entirely recumbent and branches sparingly; its method of branching does not approach the dichotomous type but is lateral and irregular. Linear series of zooecia without lateral branches are often formed.

Zooecia. The zooecia are slender and often very long; they are strongly emarginate and furrowed, and the keel that contains the furrow is conspicuous. The ectocyst is hyaline and as a rule absolutely colourless.

Statoblasts. The free statoblasts are variable in length, sometimes distinctly elongate, sometimes elongate only to a moderate degree; they are rounded at the extremities and have the sides slightly or distinctly convex outwards. The capsule is relatively large, and the free portion of the swim-ring is not much broader at the ends than at the sides. The fixed statoblasts are elongate and surrounded by an irregularly shaped chitinous membrane, which is often of considerable extent. The whole of the dorsal surface is covered with what appear to be rudimentary air-spaces some of which even contain air.

The transparent glassy ectocyst and strong furrowed keel of this species are very characteristic, but the former character is apt to be obscured by staining due to external causes, especially when the zoarium is attached to dead wood. The shape of the free statoblasts is too variable to be regarded as a good diagnostic character, but the fixed statoblasts, when they are to be found, are very characteristic in appearance. P. javanica appears to be closely related to Allman's P. dumortieri, with which stained zoaria are apt to be confused. The character of the ectocyst is, however, different, and the free part of the swim-ring is distinctly narrower at the sides of the free statoblasts. Dr. Kraepelin has been kind enough to send me one of the types.

TYPES in the Hamburg and Indian Museums.

GEOGRAPHICAL DISTRIBUTION.--Java, Penang, India. Indian localities are:--BENGAL, Calcutta; Berhampore, Murshidabad; R. Jharai, Siripur, Saran district, Tirhut: E. HIMALAYAS, Kurseong, Darjiling district (alt. 4,500 feet): MADRAS PRESIDENCY, canal near Srayikaad, Travancore. Mr. C. W. Beebe has recently sent me a specimen taken by him in the Botanical Gardens at Penang.

BIOLOGY.--Very little is known about the biology of this species. Kraepelin took it in Java on the leaves of water-lilies. It is not uncommon during the cold weather in the Calcutta Zoological Gardens on floating seeds and sticks and on the stems of bulrushes; in Travancore I took it in November on the submerged leaves of Pandani growing at the edge of a canal of slightly brackish water. Mr. Hodgart, the collector of the Indian Museum, found it in the R. Jharai on the stems of water-plants at a time of flood in the "rains." In Calcutta it is often found entangled with P. fruticosa and P. emarginata.

32. Plumatella diffusa, Leidy. (Plate IV, fig. 2.)

Plumatella diffusa, Leidy, P. Ac. Philad. v, p. 261 (1852).

Plumatella diffusa, Allman, Mon. Fresh-Water Polyzoa, p. 105 (1857).

Plumatella diffusa, Hyatt, Comm. Essex Inst. iv, pl. viii, figs. 11, 12 (1866).

Plumatella diffusa, id., ibid. v, p. 107, fig. 12 (1868).

Plumatella repens, Jullien, Bull. Soc. zool. France, x, fig. 37 (lapsus for 73), p. 110 (1885).

Plumatella diffusa, id., ibid. figs. 155, 157, pp. 130, 131.

Plumatella allmani var. diffusa, Annandale, Rec. Ind. Mus. v, p. 49 (1910).

Zoarium. The zoarium often covers a considerable area on flat surfaces and is sometimes found crowded together on the stems of plants. In the latter case the arrangement of the main branches is distinctly radiate. Upright branches occur rarely and never consist of more than three zooecia. The characteristic method of branching is best represented by the following diagram:--

The partitions are stout and numerous.

Zooecia. The great majority of the zooecia in each zoarium are distinctly L-shaped, the long limb being usually adherent. The vital organs of the polypide are contained in the vertical limb, while the horizontal one, in mature polyparia, is packed full of free statoblasts. The zooecia are cylindrical and as a rule obscurely emarginate and furrowed. The ectocyst is stiff; it is never deeply pigmented but is usually of a transparent horn-colour at the base of each zooecium and colourless at the tip, the contrast between the two portions never being very strong. The basal portion is rough on the surface, the distal portion smooth.

Statoblasts. Free statoblasts are produced in very great profusion and fixed statoblasts are also to be found as a rule. The latter resemble those of P. emarginata. The free statoblasts are never very large or relatively broad, but they vary considerably as regards size and outline. The capsule is large, the sides convex outwards and the extremity more or less broadly rounded. The air-cells are unusually large and extend over a great part of the dorsal surface of the statoblast.

Polypide. The polypide is shorter and stouter than that of P. emarginata and as a rule has fewer tentacles.

The most characteristic feature of this species is the form of the zooecia, which differ greatly from those of any other Indian species but P. allmani. In the latter they are distinctly "keg-shaped" (i. e., constricted at the base and swollen in the middle), and the zoarium never spreads out over large surfaces in the way in which that of P. diffusa does.

TYPE--? in the Philadelphia Academy of Sciences.

GEOGRAPHICAL DISTRIBUTION.--This species was originally described from North America (in which it is apparently common) and occurs also in Europe. I have seen Indian specimens from the following localities:--BENGAL, Calcutta and neighbourhood; Rajshahi (Rampur Bhulia): E. HIMALAYAS, Gangtok, Native Sikhim (alt. 6,150 feet) (Kirkpatrick, Stewart): PUNJAB, Lahore (Stephenson).

BIOLOGY.--P. diffusa in Lower Bengal is a cold-weather species. It is remarkable for the enormous number of gemmules it produces and is usually found either on floating objects such as the stems of certain water-plants, or on stones or bricks at the edge of ponds.

33. Plumatella allmani, Hancock. (Plate IV, figs. 3, 3 a.)

Plumatella allmani, Hancock, Ann. Nat. Hist. (2) v, p. 200, pl. v, fig. 3-4, pl. iii, fig. 2-3 (1850).

Plumatella allmani, Allman, Mon. Fresh-Water Polyzoa, p. 106, fig. 16 (1857).

Plumatella elegans, id., ibid. p. 107, pl. viii, figs. 6-10.

Plumatella lucifuga ("forme rampante") Jullien, Bull. Soc. zool. France, x, p. 114 (1885).

This species is closely allied to P. diffusa, from which it differs in the following characters:--

(1) The zoarium never covers a large area and as a rule grows sparingly and mainly in two directions.

(2) The zooecia are more irregular in shape, not so distinctly elbowed, smaller; they have a much more prominently keeled ridge. The great majority of them are constricted at the base and taper towards the orifice. In young zoaria they are almost colourless but in older ones there is a band of not very dense pigment round the base of the vertical limb.

(3) The free statoblasts are comparatively large and usually show a tendency to taper at the extremities, often being almost rhomboidal in form. The swim-ring does not extend so far over the dorsal surface as it does in those of P. diffusa; the "cells" of which it is composed are small.

TYPE not in existence.

I have seen every gradation between this form and Allman's P. elegans.

GEOGRAPHICAL DISTRIBUTION.--P. allmani is apparently a rare species to which there are few references in literature. It was originally described from England and is stated by Jullien to occur in France. I have found specimens only in the lake Bhim Tal (alt. 4,500 feet) in the W. Himalayas.

BIOLOGY.--The original specimens were found by Hancock on stones. My own were growing on the leaves of water-plants, usually on the under side. When the zooecia were forced to stretch across from one leaflet to another they assumed the sinuous form characteristic of Allman's P. elegans.

34. Plumatella tanganyikæ, Rousselet.

Plumatella tanganyikæ, Rousselet, Proc. Zool. Soc. London, 1907 (i), p. 252, pl. xiv, figs. 1-4.

Plumatella bombayensis, Annandale, Rec. Ind. Mus. ii, p. 169, figs. 1, 2 (1908).

Plumatella bombayensis, id., ibid. v, p. 51 (1910).

Zoarium. The whole colony is recumbent but branches freely and at short intervals in a horizontal plane, so that the zooecia become crowded together and the branches sometimes overlap one another. The zoarium often covers a considerable area, but growth seems to be mainly in two directions. When growing on the stems of water-plants the branches are often parallel and closely pressed together but remain recumbent in this position. A stout membrane sometimes extends between branches and individual zooecia.

Zooecia. The walls of the zooecia are thick, stiff, and more or less darkly but not opaquely pigmented; the external surface, although not very smooth, is always clean. The two most noteworthy characters of the zooecia are (i) their truncated appearance when the polypide is retracted, and (ii) the conspicuous, although often irregular external annulation of their walls. The tip of each zooecium, owing to the fact that the invaginated part of the ectocyst is soft and sharply separated from the stiffened wall of the tube, terminates abruptly and is not rounded off gradually as is the case in most species of the genus; sometimes it expands into a trumpet-like mouth. The annulation of the external surface is due to numerous thickened areas of the ectocyst which take the form of slender rings surrounding the zooecium; they are most conspicuous on its distal half. On the dorsal surface of the base of each zooecium there is a conspicuous furrowed keel, which, however, does not usually extend to the distal end; the latter is oval in cross-section. The zooecia are short and broad; their base is always recumbent, and, when the zoarium is attached to a stone or shell, often seems to be actually embedded in the support; the distal part turns upwards and is free, so that the aperture is terminal; the zooecia of the older parts of the zoarium exhibit the specific characters much more clearly than those at the growing points.

Polypide. The lophophore bears 20 to 30 tentacles, which are long and slender; the velum at their base extends up each tentacle in the form of a sharply pointed projection, but these projections do not extend for more than one-fifth of the length of the tentacles. Both the velum and the tentacular sheath bear numerous minute tubercles on the external surface. The base of the stomach is rounded, and the whole of the alimentary canal has a stout appearance.

A=outline of part of zoarium from a stone, × 16; B=outline of the tip of a single zooecium, × 70; C=free statoblast, × 70.]

Statoblasts. Both fixed and free statoblasts are produced, but not in very large numbers. The latter are broadly oval and are surrounded by a stout chitinous ring, which often possesses irregular membranous projections; the surface is smooth. The free statoblasts are small and moderately elongate, the maximum breadth as a rule measuring about 2/3 of the length; the capsule is relatively large and the ring of air-cells is not very much broader at the ends than at the sides; the dorsal surface of the central capsule is profusely tuberculate. The outline of the whole structure is often somewhat irregular.

In deference to Mr. Rousselet's opinion expressed in a letter I have hitherto regarded the Bombay form of this species as distinct from the African one, and there certainly is a great difference in the appearance of specimens taken on the lower surface of stones in Igatpuri Lake and of the types of P. tanganyikæ, one of which is now in the collection of the Indian Museum. The dark colour of the former, however, and their vigorous growth appear to be directly due to environment, for these characters disappear to a large extent in specimens growing on the stems of water-plants in the same lake. Indeed, such specimens are exactly intermediate between the form "bombayensis" and the typical form of the species. P. tanganyikæ is closely allied to P. philippinensis, Kraepelin, from the island of Luzon, but the latter has a smooth and polished ectocyst devoid of annulations, and zooecia of a more elongate and regular form.

TYPES of the species in the British and Indian Museums, those of P. bombayensis in the latter collection.

GEOGRAPHICAL DISTRIBUTION.--P. tanganyikæ is only known as yet from L. Tanganyika in Central Africa and from Igatpuri in the Bombay Presidency.

BIOLOGY.--In both localities the zoaria were found in shallow water. In L. Tanganyika they were encrusting stones and shells, while at Igatpuri they were fixed for the most part to the lower surface of stones but were also found on the stems of water-plants. My specimens from the Bombay Presidency were taken, on two separate occasions, at the end of November. At that date the zoaria were already decaying and large blanks, marked out by fixed statoblasts, were often observed on the stones. Probably, therefore, the species flourishes during the "rains."

35. Plumatella punctata, Hancock. (Plate IV, fig. 5.)

Plumatella punctata, Hancock, Ann. Nat. Hist. (2) v, p. 200, pl. iii, fig. 1, and pl. v, figs. 6, 7 (1850).

Plumatella vesicularis, Leidy, P. Ac. Philad. vii, p. 192 (1854).

Plumatella vitrea, Hyatt, Comm. Essex Inst. iv, pl. ix, figs. 1, 2 (1866).

Plumatella punctata, Allman, Mon. Fresh-Water Polyzoa, p. 100, fig. 15 (1857).

Plumatella vesicularis, id., ibid. p. 101.

Plumatella vitrea, Hyatt, Proc. Essex Inst. v, p. 225, figs. 18, 19 (1868).

Plumatella vesicularis, id., ibid. p. 225.

Hyalinella vesicularis, Jullien, Bull. Soc. zool. France, x, p. 133, figs. 165-172 (1885).

Hyalinella vitrea, id., ibid. p. 134, figs. 173-179.

Plumatella punctata, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 126, pl. iv, figs. 115, 116; pl. v, figs. 124, 125; pl. vii, figs. 153, 154 (1887).

Plumatella vesicularis, Braem, Unters. ü. Bryozoen süssen Wassers, p. 8, pl. i, fig. 8 (Bibl. Zool. ii) (1890).

Hyalinella punctata, Loppens, Ann. Biol. lacustre, iii, p. 163 (1908).

Plumatella punctata, Annandale, Rec. Ind. Mus. v, p. 52 (1910).

Zoarium. The zoarium is entirely recumbent and often appears to form an almost uniform flat layer instead of a dendritic body. Sometimes, however, it is distinctly linear, with lateral branches produced irregularly at considerable distances apart.

Zooecia. The zooecia differ from those of all other species in having a greatly swollen, soft ectocyst which can be transversely wrinkled all over the zooecium by the action of the muscles of the polypide and is distinctly contractile. It is mainly owing to the swollen and almost gelatinous nature of the ectocyst that the dendritic character of the zoarium is frequently concealed, for the method of branching is essentially the same as that of P. diffusa, although the zooecia are not so distinctly elbowed. The ectocyst is colourless or faintly tinted with brown; as a rule it is not quite hyaline and the external surface is minutely roughened or tuberculate. The zooecia are not emarginate or furrowed.

Statoblasts. Stationary statoblasts are not found. The free statoblasts are variable and often asymmetrical in outline, but the free portion of the swim-ring is always of nearly equal diameter all round the periphery and the capsule relatively large. Some of the statoblasts are always broad in comparison with their length.

Polypide. The polypide is comparatively short and stout. European specimens are said to have from 30 to 40 tentacles, but Indian specimens have only from 20 to 30.

Shrunken specimens of the less congested forms of this species closely resemble specimens of P. repens, but the statoblasts are more variable in shape and the ectocyst, even in such specimens, is thicker. Living or well-preserved specimens cannot be mistaken for those of any other species. Jullien regarded P. punctata as the type of a distinct genus (Hyalinella) but included in Plumatella at least one form (P. "arethusa") which probably belongs to this species. Kraepelin distinguishes as "varieties" two phases, a summer phase ("var. prostrata") and an autumn phase ("var. densa"). The former often forms linear series of considerable length with only an occasional side-branch, while in the autumn phase branching is so profuse and the branches are so closely pressed together that the zoarium comes to resemble a uniform gelatinous patch rather than a dendritic growth. A phase resembling the European autumn form is the commonest in Calcutta and I have also found one intermediate between this and Kraepelin's "var. prostrata," neither having any seasonal significance in India.

GEOGRAPHICAL DISTRIBUTION.--P. punctata is widely distributed in Europe and N. America, but in the Oriental Region it has only been found in Calcutta and the neighbourhood.

BIOLOGY.--In this part of India P. punctata flourishes both during the "rains" and in winter. I have found specimens in June and July and also in December and January. The majority of them were attached to bricks, but some were on the roots of duckweed, the stems of water-plants, and the tips of creepers falling into water. The species is often found together with Stolella indica and also with other species of its own genus. It is most common, in the neighbourhood of Calcutta, in that part of the town which is near the Salt Lakes, and occurs in ponds the water of which is slightly brackish.

Genus 2. STOLELLA, Annandale.

Stolella, Annandale, Rec. Ind. Mus. iii, p. 279 (1909).

Stolella, id., ibid. v, p. 53 (1910).

TYPE, Stolella indica, Annandale.

Zoarium. The zoarium consists of groups of zooecia (or occasionally of single zooecia) joined together by an adherent rhizome. There is no gelatinous investment.

Zooecia. The adult zooecia resemble those of Plumatella except in being sometimes more or less upright.

Polypide and Statoblasts. The polypide and statoblasts resemble those of Plumatella. Fixed as well as free statoblasts occur.

This genus is closely allied to Plumatella, from which it is probably derived. The root-like tube from which the zooecia arise is formed by the great elongation of the basal part of a zooecium, and the zoaria closely resemble those of P. punctata, for it is not until several zooecia have been produced that the characteristic mode of growth becomes apparent.

Stolella has only been found in India and is monotypic.

36. Stolella indica, Annandale. (Plate V, figs. 3, 4.)

Stolella indica, Annandale, Rec. Ind. Mus. iii, p. 279, fig. (1909).

Stolella indica, id., ibid. v, p. 53 (1910).

Zoarium. The zoarium is adherent and linear, having neither lateral nor vertical branches.

Zooecia. The zooecia are short and slender, erect or nearly so, distinctly emarginate and furrowed. Their ectocyst is soft, colourless and transparent but minutely roughened on the surface.

Polypide. The tentacles number from 30 to 35 and are rather short and stout, sometimes being slightly expanded at the tips. The stomach is comparatively short and abruptly truncated posteriorly.

Statoblasts. Both free and fixed statoblasts are found, and both are variable in form, the latter varying in outline from the circular to the broadly oval. The free statoblasts resemble those of Plumatella punctata, but are sometimes rather more elongate.

TYPE in the Indian Museum.

GEOGRAPHICAL DISTRIBUTION.--So far as we know, this species is confined to the Indo-Gangetic Plain. Major Walton found it at Bulandshahr in the United Provinces, and it is not uncommon in the neighbourhood of Calcutta.

BIOLOGY.--The zoaria of S. indica are usually fixed to the roots of duckweed or to the stems of other plants. They are often found together with those of P. punctata. A slight infusion of brackish water into the ponds in which it lives does not seem to be inimical to this species, but I have found it in ponds in which nothing of the kind was possible. It flourishes during the "rains" and, to judge from specimens kept in an aquarium, is very short-lived. Major Walton found it growing over a zoarium of Hislopia lacustris.

Subfamily B. LOPHOPINÆ.

The zoaria of this subfamily are never dendritic but form gelatinous masses which, except in Australella, are cushion-shaped or sack-like. With the possible exception of Australella, they possess to a limited extent the power of moving along vertical or horizontal surfaces, but it is by no means clear how they do so (see p. 172). The statoblasts are remarkable for their large size, and it is noteworthy that Australella, which is intermediate in structure between the Plumatellinæ and the Lophopinæ, possesses statoblasts of intermediate size. The swim-ring is always well developed, and fixed statoblasts are unknown.

Only two genera (Lophopodella and Pectinatella) have been definitely proved to occur in India, but a third (Lophopus) is stated to have been found in Madras. Should it be met with it will easily be recognized by the upright position of its polypides when their tentacles are expanded and by the fact that the statoblasts never bear marginal processes.

Genus 3. LOPHOPODELLA, Rousselet.

Lophopodella, Rousselet, Journ. Quek. Micr. Club (2) ix, p. 45 (1904).

Lophopodella, Annandale, Rec. Ind. Mus. v, p. 54 (1910).

TYPE, Pectinatella carteri, Hyatt.

Zoarium. The zoarium consists of a circular or oval mass of no great size. Polyparia do not form compound colonies.

Polypides. The polypides lie semi-recumbent in the mass and never stand upright in a vertical position.

Statoblasts. The statoblasts are of considerable size and normally bear at both ends a series of chitinous processes armed with double rows of small curved spinules.

As a rule the genus is easily recognized by means of the statoblasts, but sometimes the processes at the ends of these structures are absent or abortive and it is then difficult to distinguish them from those of Lophopus. There is, however, no species of that genus known that has statoblasts shaped like those of the Indian species of Lophopodella.

Three species of Lophopodella, all of which occur in Africa, have been described; L. capensis from S. Africa, which has the ends of the statoblast greatly produced, L. thomasi from Rhodesia, in which they are distinctly concave, and L. carteri from E. Africa, India and Japan, in which they are convex or truncate.

The germination of the gemmule and the early stages in the development of the polyparium of L. capensis have been described by Miss Sollas (Ann. Nat. Hist. (8) ii, p. 264, 1908).

37. Lophopodella carteri (Hyatt). (Plate III, figs. 4, 4a.)

Lophopus sp., Carter, Ann. Nat. Hist. (3) iii, p. 335, pl. viii, figs. 8-15 (1859).

? Lophopus sp., Mitchell, Q. J. Micr. Sci. London (3) ii, p. 61 (1862).

Pectinatella carteri, Hyatt, Comm. Essex Inst. iv, p. 203 (footnote) (1866).

Pectinatella carteri, Meissner, Die Moosthiere Ost-Afrikas, p. 4 (in Mobius's Deutsch-Ost-Afrika, iv, 1898).

Lophopodella carteri, Rousselet, Journ. Quek. Micr. Club, (2) ix, p. 47, pl. iii, figs. 6, 7 (1904).

Lophopus carteri, Annandale, Rec. Ind. Mus. ii, p. 171, fig. 3 (1908).

Lophopodella carteri, id., ibid. v, p. 55 (1910).

Zoarium. The zoarium as a rule has one horizontal axis longer than the other so that it assumes an oval form when the polypides are expanded; when they are retracted its outline is distinctly lobular. Viewed from the side it is mound-shaped. The polypides radiate, as a rule in several circles, from a common centre. The ectocyst is much swollen, hyaline and colourless.

Polypide. The polypide has normally about 60 tentacles, the velum at the base of which is narrow and by no means strongly festooned. The stomach is yellow or greenish in colour. The extended part of the polypide measures when fully expanded rather less than 3 mm., and each limb of the lophophore about the same.

Statoblast. The statoblast is variable in shape and size but measures on an average about 0.85 × 0.56 mm. The ends are truncate or subtruncate; the capsule is small as compared with the swim-ring and as a rule circular or nearly so. The processes at the two ends are variable in number; so also are their spinules, which are arranged in two parallel rows, one row on each side of the process, and are neither very numerous nor set close together; as a rule they curve round through the greater part of a circle and are absent from the basal part of the process.

A=outline of a zoarium with the polypides expanded, as seen from below through glass to which it was attached, × 4; B=outline of a zoarium with the polypides highly contracted, as seen from above, × 4; C=statoblast, × 75.]

37 a. Var. himalayana.

Lophopus lendenfeldi, Annandale (nec Ridley), J. As. Soc. Bengal, (n. s.) iii, 1907, p. 92, pl. ii, figs. 1-4 (1907).

Lophopus lendenfeldi var. himalayanus, id., Rec. Ind. Mus. i, p. 147, figs. 1, 2 (1907).

Lophopus himalayanus, id., ibid. ii, p. 172, fig. 4 (1908).

This variety differs from the typical form in having fewer tentacles and in the fact that the marginal processes of the statoblast are abortive or absent.

Pectinatella davenporti, Oka from Japan is evidently a local race of L. carteri, from the typical form of which it differs in having the marginal processes of the statoblast more numerous and better developed. The abortive structure of these processes in var. himalayana points to an arrest of development, for they are the last part of the statoblast to be formed.

TYPES. The statoblasts mounted in Canada balsam by Carter and now in the British Museum must be regarded as the types of the species named but not seen by Hyatt. The types of the var. himalayana are in the Indian Museum and those of the subspecies davenporti presumably in the possession of Dr. Oka in Tokyo.

GEOGRAPHICAL DISTRIBUTION.--The typical form occurs in Bombay, the W. Himalayas and possibly Madras, and its statoblasts have been found in E. Africa; the var. himalayana has only been taken in the W. Himalayas and the subspecies davenporti in Japan. Indian localities are:--BOMBAY PRESIDENCY, Igatpuri Lake, W. Ghats (alt. ca. 2,000 feet); the Island of Bombay (Carter): W. HIMALAYAS, Bhim Tal, Kumaon (alt. 4,500 feet).

BIOLOGY.--L. carteri is found on the lower surface of stones and on the stems and leaves of water-plants, usually in lakes or large ponds. Although the zoaria do not form compound colonies by secreting a common membrane or investment, they are markedly gregarious. The most closely congregated and the largest zoaria I have seen were assembled amongst a gelatinous green alga of the genus Tolypothrix (Myxophyceæ) that grows on the vertical stems of a plant at the edge of Igatpuri Lake; it is noteworthy that in this case the alga seemed to take the place of the common investment of Pectinatella burmanica, in which green cells are present in large numbers (p. 237). The zoaria of L. carteri are able to change their position, and I found that if a number of them were placed in a bottle of water they slowly came together at one spot, thus apparently forming temporary compound colonies. Before a movement of the whole zoarium commences its base becomes detached from its support at the anterior end (fig. 32, p. 172), but the whole action is extremely slow and I have not been able to discover any facts that cast light on its exact method of production. At Igatpuri statoblasts are being produced in considerable numbers at the end of November, but many young zoaria can be found in which none have as yet been formed.

The larva of a fly of the genus Chironomus is often found inhabiting a tube below zoaria of L. carteri. It is thus protected from its enemies but can protrude its head from beneath the zoarium and seize the small animals on which it preys.

Genus 4. PECTINATELLA, Leidy.

Cristatella, Leidy, P. Ac. Philad. v, p. 265 (1852).

Pectinatella, id., ibid., p. 320.

Pectinatella, Allman, Mon. Fresh-Water Polyzoa, p. 81 (1857).

Pectinatella, Hyatt, Proc. Essex Inst. v, p. 227, fig. 20 (1867).

Pectinatella, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 133 (1887).

Pectinatella, Oka, Journ. Coll. Sci. Tokyo, iv, p. 89 (1891).

TYPE, Pectinatella magnifica, Leidy.

This genus is closely allied to Lophopodella, from which it is often difficult to distinguish young specimens. Adult zoaria are, however, always embedded together in groups in a gelatinous investment which they are thought to secrete in common, and the statoblasts are entirely surrounded by processes that bear curved spinules at their tips only. The polypides have the same semi-recumbent position as those of Lophopodella but are larger than those of any species of Lophopodella or Lophopus yet known. The statoblasts are larger than those of any other Plumatellidæ.

The type-species was originally found in N. America but has since been taken in several localities in continental Europe. Except this and the Indian form only one species is known, namely P. gelatinosa from Japan. P. magnifica has circular statoblasts with long marginal processes, while in P. gelatinosa the statoblasts are subquadrate and in P. burmanica almost circular, both Asiatic forms having very short marginal processes.

The compound colonies formed by Pectinatella are often of great size. Those of P. gelatinosa are sometimes over 2 metres in length, while those of P. burmanica in the Sur Lake appeared to be only limited as regards their growth by the shallowness of the water in which the reeds to which they were attached were growing. Some were observed that were over 2 feet long.

38. Pectinatella burmanica, Annandale. (Plate III, fig. 5.)

Pectinatella burmanica, Annandale, Rec. Ind. Mus. ii, p. 174, fig. 5 (1908).

Pectinatella burmanica, id., ibid. v, p. 56 (1910).

Pectinatella burmanica, id., Spol. Zeyl. vii, p. 63, pl. i, fig. 3 (1910).

Zoarium. The zoaria are circular or nearly so except when about to undergo division, in which case they are constricted in the middle. As a rule they measure nearly an inch (2 cm.) in diameter. The polypides have a definite arrangement in each zoarium, being divided into four groups, each of which has a fan-like form. In the first place they are separated into two main divisions in a line running through the centre of the zoarium, and secondly each main division is separated into two subordinate ones in a line running across the other at right angles. The number of zoaria joined together in a single compound colony is very variable; sometimes there are only about half a dozen and sometimes several hundreds. The common investment in living colonies is often as much as two inches thick and has a translucent dark greenish colour due to the presence in it of green cells.

A=polypide with the lophophore expanded, × 15; a=oesophagus; b=cardiac limb of stomach; c=stomach; d=rectum; e=anus; f=funiculus. [The muscles are omitted and the external tubercles are only shown on part of the polypide. The specimen is from the Sur Lake, Orissa.] B=statoblast from Ceylon, × 35.]

Polypide. The polypide can be extruded for a distance of at least 5 mm. Its whole external surface is covered with minute tubercles. There are about 90 tentacles, which are long and slender, the velum at their base being narrow and almost straight. The stomach is of considerable stoutness.

Statoblast. The statoblasts are of large size, measuring from 1 to 1.75 mm. in diameter. In form they are almost circular, but one side is always slightly flattened. The marginal processes are very short and bear a single pair of hooks at the tip. The capsule is circular and small as compared with the free part of the swim-ring.

TYPE in the Indian Museum.

P. burmanica is evidently a near relation of P. gelatinosa, Oka, from Japan, differing from that species in the shape of the statoblasts and in having much longer tentacles. The arrangement of the polypides in the zoarium and the general structure of the statoblasts are very similar in the two species.

GEOGRAPHICAL DISTRIBUTION.--P. burmanica was originally described from a swamp at Kawkareik in the Amherst district of Tenasserim but has also been found in the Sur Lake near Puri in Orissa. Dr. A. Willey obtained specimens from a pool by the roadside between Maradankadewela and Galapitagala, at the foot of Ritigala, N. Central Province, Ceylon.

BIOLOGY.--The first specimen obtained was a statoblast fixed to a tube of the oligochæte worm Aulophorus tonkinensis taken at Kawkareik in March. At the same time young zoaria, which did not yet possess a common investment, were found on a leaf growing on a twig which drooped into the water. Large compound colonies were taken in Orissa in October. They completely encased the stems of reeds, thus forming hollow cylinders, but slipped from their supports when the reeds were pulled out of the water. In life they resembled gelatinous algæ rather than animals and exhibited a striking similarity to masses of zoaria of Lophopodella carteri surrounded by such algæ. Some of the colonies were evidently dying and contained few polypides in a living condition, but many statoblasts; others were in a flourishing condition and were producing larvæ and statoblasts simultaneously.

A piece of a colony full of larvæ was placed before midday in an aquarium, which was kept in a shady verandah. Large numbers of larvæ were set free almost immediately. They measured about 2 mm. in length and were distinctly pear-shaped; each contained a pair of polypides, which occupied a comparatively small part of the interior, the whole of the broader half being hollow. The larvæ swam slowly, broad-end-first, by means of the cilia with which their surface was covered, occasionally gyrating on their long axis and always adopting an erratic course. Towards evening they showed signs of settling down, frequently touching the glass of the aquarium with their broad ends and sometimes remaining still in this position for some minutes. Many attempts were, however, made before fixation was completed, and this did not occur until after nightfall. By next morning every larva was fixed to the glass and had everted its two polypides. Unfortunately I was not able to trace the development further, but young compound colonies were found in which the secretion of the common investment had just commenced. The zoaria in these colonies measured about 1 cm. in diameter and already contained many polypides each.

Oka has described the development from the statoblast of the allied Japanese species. He found that each statoblast produced in the first instance a single polypide, and that the statoblasts, which were produced in autumn, lay dormant through the winter and germinated in spring. As the Sur Lake begins to undergo desiccation as soon as the "rains" cease, the statoblasts in it probably do not germinate until the break of the next "rains" about the middle of June. I have had dried statoblasts in my possession for over two years. Their cellular contents appear to be in good condition, although the cells show no signs of development; but they have not germinated in my aquarium, in which some of them have now been kept for more than six months.

The green cells of the common investment are peculiar bodies that deserve further study than it has yet been possible to devote to them. Each cell is of ovoid form, varying somewhat in size but as a rule measuring about 0.03 × 0.008 mm. There can be no doubt that these bodies represent a stage in the life-history of an alga. Diatoms, bacilli and other minute plants are often present in the membrane as well as the characteristic green cells, but do not form a constant feature of it.

APPENDIX TO THE VOLUME.

HINTS ON THE PREPARATION OF SPECIMENS.

To preserve Spongillidæ.--Spongillidæ must be preserved dry or in very strong alcohol. Formalin should not be used.

To clean siliceous sponge spicules.--Place small fragments of the dried sponge (if alcohol is present, the reaction is apt to be violent) in a test tube, cover them with strong nitric acid and boil over the flame of a Bunsen burner or small spirit lamp until the solid particles disappear. Add a large quantity of water to the acid and filter through pure cellulose filter-paper, agitating the liquid repeatedly. Pass clean water in considerable quantities through the filter-paper and dry the latter carefully; place it in a spirally coiled wire and ignite with a match, holding the wire in such a way that the spicules released by the burning of the paper fall into a suitable receptacle. They may then be picked up with a camel's-hair brush and mounted in Canada balsam.

To examine the skeleton of a Spongillid.--Cut thin hand-sections with a sharp scalpel, dehydrate if necessary, and mount in Canada balsam.

To prepare gemmules for examination.--Place the gemmules dry in a watch-glass with a few drops of strong nitric acid. When gas is given off freely add water in considerable quantities. Remove the gemmules with a camel's-hair brush to clean water, then to 50%, 70%, 90% and absolute alcohol in succession, leaving them for an hour in each strength of spirit. Clear with oil of cloves and mount in Canada balsam.

To ascertain the presence of bubble-cells in the parenchyma of a Spongillid.--Tease up a small piece of the sponge with a pair of needles, mount under a thin cover-slip in strong spirit, and examine under a high power of the microscope.

To preserve Hydra in an expanded condition.--Place the polyp in a watch-glass of clean water and wait until its tentacles are expanded. Heat a few drops of commercial formaldehyde and squirt the liquid while still hot at the Hydra, which will be killed instantaneously. Remove it to a solution of formaldehyde and spirit of the following formula:--

Commercial formaldehyde 1 part. Absolute alcohol 3 parts. Distilled water 7 parts.

Then pass the Hydra through 50% and 70% alcohol and keep in 90%.

To examine the capsules of the nettle-cells.--Place a living Hydra in a small drop of water on a slide and press a thin cover-slip down upon it.

To preserve freshwater polyzoa in an expanded condition.--Place the polyzoa in a glass tube full of clean water and allow them to expand their tentacles. Drop on them gradually when they are fully expanded a 2% aqueous solution of cocaine, two or three drops at a time, until movement ceases in the tentacles. Then pour commercial formaldehyde into the tube in considerable quantities. Allow the whole to stand for half an hour. If it is proposed to stain the specimens for anatomical investigation, they should then be removed through 50% and 70% to 90% alcohol. If, on the other hand, it is desired to keep them in a life-like condition they may be kept permanently in a solution of one part of commercial formaldehyde in four parts of water. Care must be taken that the process of paralyzing the polypides is not unduly prolonged, and it is always as well to preserve duplicate specimens in spirit or formalin with the lophophore retracted.

To prepare statoblasts for examination.--Place the statoblasts for a few minutes in strong nitric acid. Then remove the acid with water, pass through alcohol, clear with oil of cloves, and mount in a small quantity of Canada balsam under a cover-slip, taking care that the statoblasts lie parallel to the latter.

ADDENDA.

The following addenda are due mainly to an expedition to the lakes of Kumaon in the W. Himalayas undertaken by Mr. S. W. Kemp in May, 1911.