CHAPTER XII. Arachnida (_continued_)—Embolobranchiata—Scorpionidea—Pedipalpi

ARACHNIDA (CONTINUED)—EMBOLOBRANCHIATA—SCORPIONIDEA—PEDIPALPI

SUB-CLASS II.—EMBOLOBRANCHIATA.

=Order I. Scorpionidea.=

Segmented Arachnids with chelate chelicerae and pedipalpi. The abdomen, which is broadly attached to the cephalothorax or prosoma, is divided into two regions, a six-jointed mesosoma and a six-jointed tail-like metasoma, ending in a poison-sting. There are four pairs of lung-books, and the second mesosomatic segment bears a pair of comb-like organs, the pectines.

The Scorpions include the largest tracheate Arachnid forms, and show in some respects a high grade of organisation. It is impossible, however, to arrange the Arachnida satisfactorily in an ascending series, for certain primitive characteristics are often most marked in those Orders which on other grounds would seem entitled to rank at the head of the group. Such a primitive characteristic is the very complete segmentation exhibited by the Scorpions. They are nocturnal animals of rapacious habit. In size they range from scarcely more than half an inch to eight inches in length. In the northern hemisphere they are not found above the fortieth parallel of latitude in the Old World, though in the New World they extend as high as the forty-fifth. A corresponding southward limit would practically include all the land in the southern hemisphere, and here the Order is universally represented except in New Zealand, South Patagonia, and the Antarctic islands.

Fossil scorpions are rarely found. The earliest examples known occur in the Silurian rocks, and belong to the genus Palaeophonus. In the Carboniferous Eoscorpius is found, and in the Oligocene Tityus.

Much remains to be discovered with regard to the habits of scorpions, and most of the isolated observations which have been recorded lose much of their value through the uncertainty as to the species concerned. The brief accounts given by Lankester and by Pocock, and the more recent and elaborate studies of Fabre, are free from this defect and contain almost the only trustworthy information we possess.

All are viviparous, and the females carry the newly-hatched young on their backs. They are predaceous, feeding for the most part on insects and spiders. These are seized by the chelate pedipalps, and, if small, are simply picked to pieces by the chelicerae and devoured, but if large the tail-sting is brought into play and the victim quickly paralysed. The process of eating is a slow one, and a Cape scorpion in captivity took two hours to devour a cockroach.

In walking, scorpions carry their pedipalps horizontally in front, using them partly as feelers and partly as raptorial organs. As regards the body the attitude varies considerably. In some cases (Parabuthus, Prionurus, etc.) it is raised high upon the legs, and the “tail” or metasoma is curved forward over the back, but in others (Euscorpius) the body is held low, and the “tail” is dragged along behind, the end only being slightly curled. In the daytime they hide away under wood or stone, or in pits which they dig in the sand. Parabuthus capensis was observed to dig a shallow pit by means of its second and third ambulatory legs, resting on its first and fourth legs aided by the chelae and the metasoma. Those that hide under wood are usually found clinging to their shelter ventral side uppermost. In captivity the creatures, though supplied with water, were never observed to drink; indeed, they are characteristic inhabitants of arid steppes and parched wastes. Like most Arachnids they can endure prolonged abstinence from food.

The only sense well developed seems to be that of touch. Notwithstanding the possession of several eyes their sight is poor. A moving object within the range of a few inches is certainly perceived, but it has to be touched before its nature is recognised. Some writers have attributed to scorpions a keen sense of hearing, and so-called “auditory hairs” are described on the tibia of the pedipalp, but Pocock came to the conclusion that Parabuthus capensis and Euscorpius carpathicus were entirely deaf, and Lankester could obtain no indication of auditory powers in the case of Prionurus. The sense of touch is extremely delicate, and seems to reside in the hairs with which the body and appendages are more or less thickly clothed. The pectines are special tactile organs. That they are in some way related to sex seems probable from the fact that they are larger in the male and sometimes curiously modified in the female, but they appear to be of use also in determining the nature of the ground traversed by the animal, being long in such species as raise the body high on the legs, and short in those that adopt a more grovelling posture. Pocock noticed that a scorpion which had walked over a portion of a cockroach far enough for the pectines to come in contact with it immediately backed and ate it.

FIG. 167.—Buthus occitanus in the mating period. (After Fabre.) ]

As is the case with most poisonous animals, their ferocity has been much exaggerated; they never sting unless molested, and their chief anxiety is to slink off unobserved. The fables that they kill their young, and that when hard pressed they commit suicide by stinging themselves to death, perhaps hardly deserve serious consideration. The latter accusation is disproved by the fact that a scorpion’s poison has no effect upon itself, or even upon a closely allied species. Some writers think that in the frantic waving of the “tail,” which is generally induced by strong excitement, a scorpion may sometimes inadvertently wound itself with the sharp point of its telson.

Fabre gives a fascinating account of the habits of Buthus occitanus, which occurs in the south of France. He found these scorpions plentifully in arid, stony spots exposed to the sun. They were always solitary, and if two were found under the same stone, one was engaged in eating the other. Their sight is so poor that they do not recognise each other without absolute contact.

Fabre established colonies in his garden and study, providing them with suitable soil and sheltering stones. They dug holes by reducing the earth to powder by means of the three anterior pairs of legs—never using their pedipalpi in the operation—and sweeping away the débris with the tail. From October to March they ate nothing, rejecting all food offered to them, though always awake and ready to resent disturbance. In April appetite seemed to awaken, though a very trifling amount of food seemed to suffice. At that time, too, they began to wander, and apparently without any intention of returning, and they continued daily to escape from the garden enclosure until the most stringent measures were taken to keep them in. Not till they were surrounded by glass and the framework of their cages covered with varnished paper were their attempts to climb out of their prison frustrated. Fabre came to the conclusion that they took at least five years to attain their full size.

FIG. 168.—The “promenade à deux” of Buthus occitanus. (After Fabre.) ]

His most interesting observations were concerned with their mating habits, in connection with which he noted some extraordinary phenomena. After some very curious antics, in which the animals stood face to face (Fig. 167) with raised tails, which they intertwined—evidently with no hostile intention—they always indulged in what Fabre calls a “promenade à deux,” hand in hand, so to speak, the male seizing the chelae of the female with its own, and walking backwards, while the female followed, usually without any reluctance. This promenade occupied an hour or more, during which the animals turned several times. At length, if in the neighbourhood of a suitable stone, the male would dig a hole, without for a moment entirely quitting its hold of the female, and presently both would disappear into the newly-formed retreat.

After mating, the male was often devoured by the female. Moreover, after any combat with an enemy, such as a Lycosa or a Scolopendra, it appeared to be de rigueur to eat the vanquished, and on such occasions only was any considerable amount of food consumed.

The scorpions were not, however, anxious to fight, greatly preferring to retire if possible; but when incited to combat, their sting was quickly fatal to any mature insect, to spiders and to centipedes. Curiously enough, however, insect larvae, though badly wounded, did not succumb to the poison. Newly-hatched scorpions mounted on the mother’s back, where they remained motionless for a week, entirely unfed. They then underwent a moult, after which they were able to forage for themselves.

=External Structure.=

The chitinous plates of the prosoma are fused to form a carapace. Six segments are clearly indicated by the six pairs of appendages, but, though the development of Scorpio affords little direct evidence of the fact, there is reason to believe that there once existed a pre-cheliceral segment, as has been clearly proved in the case of the spiders. An embryonic pregenital segment has also been recognised. The six prosomatic appendages are those proper to the Arachnida, being the chelicerae, pedipalpi, and four pairs of ambulatory legs. The mesosoma, which is broadly attached to the prosoma, comprises six segments, indicated ventrally by the genital operculum, the pectines, and the four pairs of pulmonary stigmata. The last of the broad abdominal segments, which tapers abruptly, belongs to the metasoma, which also comprises six segments, and is succeeded by the post-anal spine or sting.

=Prosoma.=—Near the middle of the carapace are two median eyes, and on its antero-lateral borders are usually to be found groups of smaller eyes, numbering from two to five. All the eyes are simple. There is a difference, however, in their development, the median eyes being diplostichous, or involving two layers of hypoderm, while the lateral eyes are monostichous, and pass through a stage strikingly like the permanent condition of the eyes of Limulus. The arrangement of various slight longitudinal ridges on the dorsal surface of the carapace is of systematic importance. On the ventral surface, just in front of the genital operculum, is a sternum, never large, and sometimes barely visible. Its shape and size constitute one of the principal family characteristics.

FIG. 169.—Buthus occitanus. =A=, Dorsal view; =B=, ventral view. (After Kraepelin.) ]

=Mesosoma.=—The dorsal plates or terga are distinct, and are connected by soft chitin with their corresponding sterna.

Beneath the second abdominal segments are borne the “pectines” or comb-like organs. In their structure four portions are distinguishable, an anterior lamella or shaft attaching them to the body, a middle lamella, the teeth, and the fulcra, a series of small chitinous pieces intercalated between the bases of the movable teeth.

Beneath the third, fourth, fifth, and sixth segments are the paired openings of the lung-sacs.

=Metasoma.=—The first segment is usually and the remainder are invariably enclosed in complete chitinous rings and show considerable variations in their comparative size and shape, and in the arrangement of the ridges and keels with which they are usually furnished. The post-anal segment is more or less globular at its base, constituting a “vesicle,” and terminates in a fine curved point, the “aculeus,” perforated for the passage of the delicate poison-duct. With the abdomen fully extended the point is directed downward, but in the attitude of attack or defence, when the “tail” is carried horizontally over the back, the sting points forward in the neighbourhood of the animal’s head.

FIG. 170.—=A=, Diagram of a Scorpion’s leg; 1, coxa; 2, trochanter; 3, femur; 4, patella; 5, tibia; 6, protarsus; 7, tarsus; p.s, pedal spur; t.s, tibial spur. =B=, Fourth tarsus of Palamnaeus swammerdami; l, lateral lobe. (After Pocock.) ]

=Appendages.=—The three-jointed chelicerae are powerful and chelate. The first joint is small, but the second is strongly developed and bears at its anterior end on the inner side a projection which forms the immovable finger of the chela. The third joint, or movable finger, is articulated on the outer side, and both fingers are armed with teeth whose arrangement is useful in distinguishing the species. The pedipalpi consist of six joints. The coxa is small and has an inwardly directed lamella which assists in feeding. The trochanter is also a small joint, bearing, normally at right angles to the longitudinal axis, the powerful humerus or femur. Then follows the brachium or tibia, again directed forward, and the last two joints form the chela or “hand,” the terminal joint or movable finger being on the outer side as in the chelicerae. In systematic determination special attention is given to the “hand.” In some forms the upper surface is uniformly rounded, while in others a “finger-keel” divides it into two flattish surfaces almost at right angles. The biting edges of the fingers are usually furnished with rows of minute teeth arranged characteristically in the different genera. The ambulatory legs are seven-jointed, though, unfortunately, authors are not agreed upon the nomenclature of the joints. Kraepelin names them coxa, trochanter, femur, tibia, and three-jointed tarsus, and Simon agrees with him. Pocock’s names are coxa, trochanter, femur, patella, tibia, protarsus, and tarsus, and it is certainly convenient that each joint should have a separate name, but it must be borne in mind that the tibia of different authors is not always the same joint. Special attention must be directed to the three terminal joints, which furnish highly important characteristics. The tibia (in Pocock’s sense) is sometimes provided with a “tibial spur” at its lower distal extremity. From the soft arthrodial membrane between the protarsus and tarsus may proceed one or more dark-tipped claw-like spurs, the “pedal spurs.” The terminal joint (tarsus of Pocock) is variously furnished with hairs and teeth, and always ends in a pair of well-developed movable claws beneath which a much reduced and sometimes almost obsolete third claw is distinguishable. The tarsus generally projects in a “claw-lobe” over the base of the superior claws, and sometimes lateral lobes are present. The first and second coxae have triangular maxillary lobes directed towards the mouth. The third and fourth coxae are fused together on each side, and those on one side are separated from those on the other by the sternum. In other respects the four pairs of legs are usually similar.

=Internal Anatomy.=

The =alimentary canal= is a fairly uniform tube, nowhere greatly dilated. The very small mouth leads into a small suctorial chamber, and this is connected by a narrow oesophagus, which pierces the cerebral nerve-mass, with a slightly dilated portion which receives the ducts of the first pair of gastric glands, often called salivary glands. The succeeding portion in the prosoma receives four or five more pairs of ducts from the well-developed gastric glands. In the rapidly narrowing first metasomatic segment the intestine receives one or two pairs of Malpighian tubes, and thence proceeds to the anus, situated ventrally in the last segment.

The =vascular system= is of the usual Arachnid type, the heart being a seven-chambered dorsal longitudinal vessel lying in a pericardium, with which it communicates by seven pairs of valvular ostia. Lankester has demonstrated several pairs of superficial lateral veins connecting two deep-seated ventral venous trunks with the pericardium. The lung-books are, so to speak, pushed in to dilatations of these trunks, so that some of the lateral veins carry blood newly aerated by the lung-books directly to the pericardium.

The =nervous system= is not greatly concentrated except in the prosoma, where there is a single ganglionic mass which innervates not only the whole prosoma but the mesosoma as far as the first and sometimes the second pair of lung-books. There are two mesosomatic ganglia, variously situated in different genera, and each metasomatic segment has its ganglion.

The =generative organs= are more or less embedded in the gastric glands. There are two testes, each composed of a pair of intercommunicating tubules, and connected by a common vas deferens with the generative aperture, which is furnished with a double protrusible intromittent organ. A pair of vesiculae seminales and a pair of accessory glands are also present. The female possesses a single ovary, consisting of a median and two lateral tubules, all connected by cross branches.

In addition to the external sclerites a free =internal skeletal plate=, situated in the prosoma between the alimentary canal and the nerve-cord, furnishes convenient fulcra for muscular attachment. It is known as the “endosternite.”

Brauer has made the most complete study of the development of Scorpio, and two of the most interesting of his conclusions may be mentioned here. He has shown the lung-books to be derived from gills borne on mesosomatic appendages. Moreover he found in the embryo five pairs of segmental ducts—in segments 3–6 and 8—and demonstrated that those of segment 5 persisted, though without external aperture, as coxal glands, and those of segment 8 as the genital ducts.

=Classification.=

More than 350 species of scorpions have been described, but many of these are “doubtful,” and probably the number of known forms may be put at about 300. These are divided by Kraepelin into six families and fifty-six genera. The best indications of the family of a scorpion are to be found in the shape of the sternum, the armature of the tarsi, and the number of the lateral eyes, while assistance is also to be derived from the shape of the stigmata and of the pectines, and from the absence or presence of a spine beneath the aculeus.

The six families are: Buthidae, Scorpionidae, Chaerilidae, Chactidae, Vejovidae, and Bothriuridae.

=Fam. 1. Buthidae.=—Sternum small and generally triangular. Tibial spurs in the third and fourth legs. Generally a spur beneath the aculeus. Lateral eyes three to five in number.

There are two sub-families: BUTHINAE and CENTRURINAE.

The BUTHINAE, which possess a tibial spur, comprise fourteen genera, most of them Old World forms. The principal genera are Buthus, which contains about 25 species, and Archisometrus with 20 species. One genus only, Ananteris, is South American, and it includes only a single species. The genus Uroplectes, with 16 species, is almost entirely African.

The CENTRURINAE, without tibial spur, are New World scorpions, though Isometrus europaeus (maculatus) is cosmopolitan. The principal genera are Tityus with 30 species, Centrurus with 13, and Isometrus with 6.

=Fam. 2. Scorpionidae.=—Sternum broad and pentagonal, with sides approximately parallel. No tibial spur, but a single pedal spur. Generally three lateral eyes.

Nearly a hundred species of Scorpionidae have been described, distributed among fifteen genera. The following sub-families are recognised: Diplocentrinae, Urodacinae, Scorpioninae, Hemiscorpioninae, and Ischnurinae.

The DIPLOCENTRINAE have a spur under the aculeus. They form a small group of only eight species. The principal genus, Diplocentrus, is entirely Neotropical, but Nebo has a single Old World representative in Syria.

The URODACINAE, with the single genus Urodacus, are Australian scorpions. As in the next sub-family, there are rounded lobes on the tarsi, but there is only a single keel on the “tail,” and the lateral eyes are two in number. Six good and three doubtful species are recognised.

The SCORPIONINAE are Asiatic and African forms, and are recognised by the tarsi having a large lobe on each side, by the convex upper surface of the “hand,” by the presence of two median keels on the “tail,” and by the possession of three lateral eyes. Palamnaeus (Heterometrus) has sixteen species in the Indian region. There are about thirty species of Opisthophthalmus, all natives of South Africa. Pandinus includes about ten species, but there are only two species of the type genus Scorpio, S. maurus and S. boehmei.

The sub-family HEMISCORPIONINAE was formed for the reception of the single Arabian species Hemiscorpion lepturus. Its most striking characteristic is the cylindrical vesicle of the tail in the male.

The ISCHNURINAE differ from the Scorpioninae chiefly in the absence of the tarsal lobes, the presence of a well-marked finger-keel, and the generally more depressed form of the body and hand. In the opinion of some authors they should be separated from the Scorpionidae as a distinct family, the Ischnuridae. There are more than twenty species, divided among six genera. The type genus Ischnurus has only the single species I. ochropus. There are eight species of Opisthacanthus, which has representatives in Africa and America.

=Fam. 3. Chaerilidae.=—Sternum pentagonal with median depression or “sulcus” rounded posteriorly. Two pedal spurs. Stigmata circular. Two lateral eyes with a yellow spot behind the second. Pectines very short.

This small family has the single genus Chaerilus with but seven species, natives of the Oriental region.

=Fam. 4. Chactidae.=—Two pedal spurs. Two lateral eyes (or, rarely, no eyes) but without yellow spot. Characteristic dentition on movable finger of “hand.”

There are three sub-families, Megacorminae, Euscorpiinae, and Chactinae.

The MEGACORMINAE include but a single Mexican form, Megacormus granosus. There is a single toothed keel under the “tail,” and all the under surface is spiny. There is a row of long bristles under the tarsus.

In the EUSCORPIINAE the upper surface of the hand is divided into two surfaces almost at right angles by a strong finger-keel. This is a small group of about six species found in the Mediterranean region. The two genera are Euscorpius and Belisarius.

The CHACTINAE are without any marked keel on the hand. The scorpions of this sub-family are found in equatorial South America and the West Indies, where there are more than twenty species divided about equally between the four genera Chactas, Broteas, Broteochactas, and Teuthraustes.

=Fam. 5. Vejovidae.=—No tibial, but two pedal spurs. A single row of hairs or papillae under the tarsus. Sternum generally broader than long. Elongate stigmata, and three lateral eyes.

Seven of the eight genera of this family include only American forms, the principal genus being Vejovis, with about ten species. The genus Scorpiops, however, belongs to the Indian region and numbers more than ten species.

=Fam. 6. Bothriuridae.=—Sternum much reduced and sometimes hardly visible, consisting of two slight, nearly transverse bars.

Of the seven genera of this family one, Cercophonius, is Australian. The other six genera include some dozen South American forms, Bothriurus having four species.

=Order II. Pedipalpi.=

Arachnids with non-chelate, two-jointed chelicerae, powerful pedipalpi, and four pairs of legs, of which only the last three are ambulatory, the first being used as tactile organs. The cephalothorax is usually covered by an undivided carapace, but the pedunculated abdomen is segmented. Respiration is by lung-books.

The Pedipalpi are a little-known group of animals of nocturnal habits. Though rarely seen they are widely distributed, being found in India, Arabia, the greater part of Africa, and Central and South America. They are of ancient origin, a fossil genus, Graeophonus, of the Tarantulidae (Phrynidae, see p. 312), occurring in the Carboniferous strata in North America. They live under stones and bark, and in caves, where, when disturbed, they seek safety in crannies in the rock.

Little is known of their habits, but they are believed to feed chiefly upon insects. The female Tarantula carries the developing eggs, somewhat after the manner of the Chernetidea (see p. 434), in a bag beneath the abdomen, the under surface of which becomes concave and dome-like during the period of gestation.

FIG. 171.—Thelyphonus, diagrammatic ventral view; about natural size. c, Coxal joint of pedipalp; g, generative opening; p, pedipalp; sp, spiracles; st, sternal plates; 1, 2, 3, 4, ambulatory legs. (After Pickard-Cambridge.) ]

=External Structure.=—The external features which the members of this Order have in common are the segmented pediculate abdomen (9 to 12 segments), the two-jointed non-chelate chelicerae, the antenniform first pair of legs, and the presence of two pairs of lung-book stigmata beneath the abdomen. The constituent families differ so much in outward form that they must be dealt with separately.

The Thelyphonidae or “Whip Scorpions” (see p. 312) have a long-oval carapace bearing well-developed eyes, two in front, and a group of three or five on either side some distance behind. The pedipalpi are chelate, and have their basal joints fused beneath the mouth, being thus incapable of any masticating motion.

The first legs are six-jointed, and have multi-articulate tarsi; the others are seven-jointed, and their tarsi, in some species at least, are tri-articulate. The abdomen consists of two portions, a wide nine-jointed pre-abdomen and a short narrow three-jointed post-abdomen, to which a filiform tail is articulated. Beneath the cephalothorax, between the coxae of the legs, is a distinct sternal plate in two portions (Fig. 171). The first abdominal ventral plate is largely developed, and covers two segments. Behind it are the median genital opening and two pulmonary stigmata, while the other stigmata are behind the second ventral plate, which corresponds to the third abdominal segment. On the last abdominal segment there are often two or four light-coloured spots called “ommatoids,” and considered by some authors to be organs of sight. Laurie, however (vide infra), thinks it more probable that they are olfactory in function.

The Schizonotidae (see p. 312) have a two-jointed carapace, and do not possess more than two eyes. There is a short unjointed tail-piece.

In the Tarantulidae (Phrynidae) the whole body is much flattened and extended laterally, the undivided carapace being reniform, and broader than long. The long non-chelate pedipalps have their basal joints free and movable, and there are several sternal plates. There are nine abdominal tergal plates, the last three diminishing rapidly in size, and the last plate covering a button-like terminal portion of the abdomen. The first abdominal ventral plate is largely developed, as in the Thelyphonidae, and the genital orifice and pulmonary stigmata are in the same situation as in that group. The Tarantulidae have glutinous glands in the first abdominal segment which are capable of spinning a few irregular threads.

In the whole group paired circular depressions are conspicuous dorsally on all the abdominal segments. These indicate the points of attachment of the dorso-ventral muscles.

=Internal Structure.=—The anatomy of the Pedipalpi has been very inadequately studied. Disconnected notes on various points of structure have been published by various morphologists, but no complete investigation has yet been made of the internal organs. This is largely due to the difficulty of obtaining material, and the bad state of preservation of the internal parts of such specimens as have been available for dissection.

The following points have been made out in the anatomy of Thelyphonus.

The alimentary canal commences after the mouth with a pharynx which, though not dilated, is furnished with sucking muscles. It then narrows into an oesophagus which passes through the nerve-mass, and afterwards dilates to form the mid-gut, which immediately gives off two large lateral diverticula which extend backwards, each having five lobes. There are also two median diverticula which proceed from the ventral surface and pass through the endosternite. The abdominal portion of the canal is entirely concealed by the great “liver” mass which communicates with it by four paired ducts in the anterior part of the abdomen. Behind the fourth abdominal segment the gut is narrow till it expands in the seventh segment into an hour-glass-shaped stercoral pocket which, according to Laurie, is a portion of the mesenteron.

The excretory organs are the Malpighian tubes and the coxal glands. The former are generally described as entering the anterior portion of the stercoral pocket, but according to Laurie they pass along its ventral surface, attached to it by connective tissue, and really enter at the posterior end. The coxal glands are well developed, and lie beneath the endosternite, opening near the first coxae.

The nervous system is much concentrated and of the usual Arachnid type. The median abdominal nerve has a ganglion towards its extremity, supplying, according to Bernard, the muscles which move the tail. The heart is extremely long, and varies little in width. It has nine pairs of ostia—two in the thorax and seven in the abdomen. The generative glands are paired, and in the male there are large seminal vesicles. In the most ventral portion of the abdominal cavity lies a remarkable asymmetrically-situated gland, the “stink-gland.” It consists of a number of secretory tubules communicating with two elongated sacs, one of which lies beneath the nerve-cord, and therefore medially, while the other lies far to the left. Their ducts proceed to the anus or its vicinity.

The caudal organs, or white spots which, as already mentioned, are usually found on the last of the three post-abdominal segments of Thelyphonus, are of doubtful function. They have been variously explained as the stink-gland orifices, and as organs sensitive to light (“ommatoids”). Laurie was unable to find any pore in this region, nor was there any of the pigment so characteristic of organs of sight. The histological structure indicated a sense-organ rather than a gland, but the use of these organs is entirely conjectural.

=Classification.=—The order Pedipalpi is divided into three families— Thelyphonidae, Schizonotidae and Tarantulidae. The first two are considered by some authors to form a sub-order, UROPYGI, or tailed Pedipalpi, while the Tarantulidae constitute the remaining sub-order AMBLYPYGI, the members of which are tailless.

=Fam. 1. Thelyphonidae.=—This family comprises nine or more genera, differing chiefly in the position of the eyes, the structure of the genital operculum, the armature of the pedipalps, and the presence or absence of “ommatoids” in the anal segment.

The three following genera are among those most likely to be met with. Two ommatoids are present in each.

Thelyphonus has a spine on the second ventral plate, and a deep median impression on the male genital operculum, which is, however, absent from that of the female. There are about fifteen known species of this genus, inhabiting Southern Asia and the East Indies.

Typopeltis has ridges running forward from the lateral eyes. The middle third of the female operculum is raised and deeply impressed in the middle. This genus is represented in China and Japan. Mastigoproctus has a short and stout coxal apophysis of the pedipalp, without a tooth on its inner side. It is found in Mexico, Brazil, and the West Indies. Other genera are Thelyphonellus (Demerara), Labochirus (Ceylon), Hypoctonus (Burma), Mimoscorpius (Philippines), Uroproctus (Assam), Abalius (New Guinea), without ommatoids, and Tetrabalius (Borneo), with two pairs of ommatoids.

=Fam. 2. Schizonotidae (= Tartaridae).=—This family contains only two genera, Schizonotus (= Nyctalops, Pickard-Cambridge, nom. preocc. Aves) and Trithyreus (= Tripeltis, Thorell, nom. preocc. Reptilia). They are very small, pale-coloured forms (about 5 mm. in length), found in Burma and Ceylon.

=Fam. 3. Tarantulidae=, better known as =Phrynidae=. Pocock has shown that Fabricius established the genus Tarantula from the species T. reniformis in 1793, while there is no earlier record of Olivier’s Phrynus, established for the same species, than Lamarck’s citation of it in 1801. The family is divided into three sub-families, Tarantulinae, Phrynichinae, and Charontinae.

(i.) The TARANTULINAE are new-world forms, represented by three genera, Tarantula, Acanthophrynus (Phrynopsis), and Admetus (Heterophrynus), in Central and South America and the West Indies.

(ii.) The PHRYNICHINAE belong to the Old World, being found in Africa, India, and Ceylon. Phrynichus, Titanodamon and Nanodamon are genera of this sub-family.

(iii.) The CHARONTINAE are natives of South-East Asia and the Pacific Islands. There are five genera and eight species.