Part 2

I am now, therefore, writing about our British land shells, "slugs and snails" in common speech, with the hope that it may add a new interest to the country walks of lads and lasses.

I could show you a wall-case I made for a school. It contains specimens of all the British land shells with the exception of the slugs, which (with the exception of one of which I shall speak in its place) have no external or covering shell, although a small sort of shell, or at any rate some chalky grains, is found inside most of them. You would see that some are as small as a pin's head although full grown, and they would require a magnifying glass to distinguish one from the other. The largest is Helix pomatia (figured on pp. 11 and 12), which often goes by the name of "the edible snail." All snails are edible and nutritious; but this is the one cultivated in snail farms and sold as food abroad. Sometimes it is called "the Roman snail," from an idea, probably wrong, that it was introduced by Cæsar's soldiers, although as a matter of fact it is unknown in South Italy. Sometimes also it is called "the apple snail," partly because it is as large as a middle-sized apple, and partly because people thought the name pomatia came from the Latin pomum, "an apple," whereas it really comes from the Greek [Greek: pôma]. This word means a lid, or closing arrangement, and this mollusc makes a hard front door for itself when it hibernates, i.e. suspends active life and buries itself in the winter.

It is much to be regretted that in most cases scientific names fail to give much information to the young student, and in some cases they give none at all. The first or generic name is supposed to be formed from Greek, the second, or specific, from the Latin, but there are some hybrids and many mere "nonsense names" to puzzle beginners. Thus the slug Limax gets its name from limus, "mud"; but a scientist, who ought to have known better, when wanting a name for another kind of slug, transposed the initial letters and made Milax! Vitrina is a sensible and descriptive name, the Latin for glassy, given to a shell like thin glass; but the Greek Arion recalls either a certain musician or a certain swift steed, neither of whom naturally suggests a slug. For Balea at least four derivations have been suggested--none of them probable. Two facts concerning the life or appearance of a mollusc we should learn from its two names, but this is not the case with Agriolimax agrestis, which is by interpretation "the field slug inhabiting fields." Nor are we helped by the specific name virgata or striped when so many land shells are striped or banded, and still less by terrestris for one land shell when all land shells are terrestrial.

You would note, however, in this wall-case that the species are not many (a good many of the specimens are varieties, not separate species), and that, therefore, one can collect with the hope of speedily forming a complete collection without that inevitable absence of finality found when one collects postage stamps, or, still more, picture postcards, of which one might secure thousands, only to find that fresh thousands were brought out next year. Here, however, is no impossible ideal of perfection. There are but eighty-two land and forty-five freshwater shells in Britain.

Let us imagine we are starting for an afternoon snailing near London. Which way? To Oxshott? To Caterham? To the latter for choice, since it is on the chalk, whereas the former is on the sand. Snails require lime to make shells, and only on chalk or limestone will you find an abundance. Here, too, as at Box Hill, we shall find the big Helix pomatia, only found in a few English counties, and very local there. If we were very fortunate, we might find a sinistral, or "left-handed" specimen. In the case of the pomatia on the right hand there is shown the thick epiphragm which the mantle secretes before the mollusc hibernates. It hardens on exposure to the air like plaster-of-paris; but is not a true operculum, for that is a constant possession of the shells which have it. Opercula are mainly found in marine or fluviatile shells, and may be either horny (like the winkle) or stony. Amongst our British land shells Cyclostoma elegans and Acicula lineata alone have true opercula, though others form some thin epiphragm for the exclusion of cold air and enemies when they hibernate.

Most shells grow to the right, and a freak which does the contrary is so rare that of the millions of the common H. virgata that I have seen and handled, only one delighted me with its left-handedness. If it is early summer (nearly all snails hide, burrow, and sleep during the winter), look about on the grass for some half-chalky, half-stony shields, which are the winter front doors of H. pomatia, now discarded; while sharper eyes might even descry the flinty little darts with which they have been love-making. The illustration on p. 15 shows three of these darts, much magnified. Only the most highly developed Helices possess these courting weapons, not unlike bayonets in form, sometimes rounded and smooth, and sometimes with two or even four lateral blades, so that the section of the dart of H. pomatia is in the form of a Greek cross. Not many British shells have these darts, but in one case their study is useful, since H. nemoralis and H. hortensis, though so closely allied that early conchologists considered them to be of the same species, have darts remarkably distinct one from the other, so that they become a court of final appeal if from outward appearance it is difficult to distinguish, say, a white-mouthed nemoralis from a dark-mouthed hortensis.

Whenever you see a stone, a brick, a branch of dead wood, or even an old boot or a piece of newspaper in the hedge or on the grass, turn it over, for many of the smaller shells are thus found, and "leave no stone unturned" is eminently a motto for the conchologist. Some of the shells will be tiny, and must be studied under a magnifying glass--which all naturalists should always have in their pockets--or even under a microscope at home, in order to discover, not only their beauty of marking or sculpture, but even to what species they belong.

When you see a man sweeping herbage with a net, or beating hedges and shrubs over an inverted umbrella, he is probably an entomologist in search of caterpillars or beetles; but the same methods will often reward the snail-hunter.

Especially in the hedges will you find the two allied species Helix (Cepea) nemoralis and hortensis, to which the attention of beginners should first be directed, inasmuch as they are so common, so beautiful, and so varying both in colour and the number of the chocolate bands they usually bear. See the illustration of some of these at rest on hawthorn, p. 17. Canary-yellow, flesh-colour, chocolate, and almost white, are the prevailing ground-colours. Five is the normal number of bands on the largest or body-whorl, although sometimes all run into one, and often one, some, or all are wanting. Where only one band is found--throughout the Helicidæ--it is usually that on the periphery or middle of the whorl, and a shell in which this band is wanting, while others are found, is a rarity. People are usually astonished, on seeing a good series of the colour and variations of these two shells, how they vie with those of warmer regions.

Next search trunks of trees, and especially the smooth boles of the beeches. The rough bark of the elm or oak is not congenial to slugs or snails. Where trees are moss-covered at their foot, or walls at their top, many of the smaller shells may be expected; while handfuls of dead leaves may be shaken over something white, or taken home in a large bag to be treated there. Hurdles leaning against a hedge are often found to bear a good crop of snails. Damp places must be sought in dry weather; but a rainy day, that troubles some kinds of naturalists, sends the conchologist forth rejoicing, especially if a warm evening follows a wet day. A night search with a lantern will often be profitable. Where they will be undisturbed, traps may be set, such as flat pieces of wood (the older the better), or cardboard, lying on the grass; while most of those species that belong to the group which seems to prefer the sun, e.g. H. itala, virgata, etc., are fond of a newspaper for food rather than for shelter.

During the hibernating season, which extends from November to April, we turn rather to ditches than to hedges, and, armed with a perforated scoop at the end of a long stick, we dredge among the water-weeds, or sift, like gold-washers, the sand or mud in ditches, ponds, and backwaters of rivers. Here we are introduced to the great bivalve family which is unknown on land, and our trophies range from the freshwater mussels, as large as our hand, to others hardly larger than a pin's head. These must be sought at the bottom; but on the weeds, or on the bottom, will be found not a few species of gasteropods or univalves, some of which we may have noticed in a freshwater aquarium. These, of course, are closely connected with the land shells, which the bivalves are not. They can be brought home alive in a tin box with a little moss, whereas for the land shells a calico bag with a little foliage therein is best. In both cases some small glass tubes with corks should be brought in a tin box in order to keep safely and separately the tinier kinds. You can often discover what small shells inhabit a particular ditch or pond by noticing the cases of caddis-worms, some of which are formed almost entirely of shells instead of vegetable fragments.

Using the precious gift of observation, we have found our shells; at home we exercise the other gifts of comparison and order, in the preparation and arrangement of our collection. A dash of quite boiling water kills instantaneously any molluscs whose shells we want to preserve, and then the body is extracted after the fashion observed with regard to winkles at tea. Be careful to get out all the body of the animal, and then it is well to wash out any slime or particles by directing a fine but strong jet of cold water into the shell. This can be done by holding your thumb nearly over the mouth of a watertap, while the shell is held in the left hand. Only adult shells should usually be taken, and those which are weather-worn or bleached should be neglected. In most the lip, or opening, of the shell will be hard if adult, and membranous if young; but experience alone will enable you to discriminate, especially where the young of one species is like the adult of another.

Get into the way of carrying a note-book with you to record not only what shells, or varieties of a species, are found in any particular spot, but also anything you observe as to the habits or peculiarities of the objects of your search. Notes as to protective colouring or mimicry; the influences of a wet or a dry season on the relative thickness of shells; the difference in size caused by abundance or scarcity of diet; what plants are preferred and what avoided as food by particular helices,--are some of the points of interest, apart from the earliest and latest dates at which certain species are abroad and active.

If you possess, or borrow, a microscope, many new wonders and fresh lines of inquiry will open out. I know one professor who devotes himself to the study of the teeth of molluscs. A snail may possess over twenty thousand tiny flinty teeth set on a ribbon so as to make a mowing-machine for the vegetable matter on which it feeds. With its aid also you might study the life-history of a mollusc from the egg onwards, and be able to determine by minute anatomical points whether two molluscs were of the same species or not--a matter in which the shape or appearance of the shell is not always a safe guide.

Here, then, is a new hobby for some of my readers, or, at any rate, a fresh source of interest when they are in the country. If any collector lives near you, I am sure he or she would be delighted to have your company during an expedition, and you would learn more by sight and hearing than by reading. If, however, you must fall back upon a book, get The Collector's Manual by L. E. Adams, published by Taylor Bros., Leeds. This is invaluable both to the beginner and to the owner of a good collection.

From this I borrow by leave the plate on p. 22, which will enable the beginner to understand from the first certain names of parts of the shell or the body of the bivalve, univalve, or slug which otherwise might not be clear. The "muscular scars" are indents in the shell which mark where the muscles were fixed whose function was to bring close together the two valves of the shell when it has need to exclude air or enemies.

The figures of the snail and the slug below are introduced to give further knowledge of the soft parts. B is the body, soft and with a surface generally wrinkled or covered with small tubercles. F is the foot or muscular pad which forms the foot by the wavelike contractions of which it moves. H is the head, bearing the tentacles T{1} and T{2}, of which the upper pair have the eyes, E. The mantle, M, makes the shell by secreting lime, etc. In it is the breathing orifice, BO, obvious in the slug, but in the snail nearly hidden by the shell. L in the snail is the spiral part, the liver, and it occupies a large part of the shell.

Without going into details of classification and anatomy, which would only deter or puzzle a beginner, let me take two typical molluscs of those which we shall find in England, the common garden snail Helix aspersa, and a freshwater mussel, Unio margaritifer, and see where they come in the scale of creation and what are their powers and peculiarities.

Molluscs (mollis esca, soft food--boneless creatures) are below the aristocracy of the vertebrates or backboned creatures, and so they come just below the Fishes, but above the Insects. They are divided into those possessing a head and those possessing no head (although with some sort of a brain or organ of sense), the snail being of the former class and the mussel of the latter. The former are univalves and the latter bivalves having two shells for protection. The latter also are restricted to life in water, whereas the former are found both on land and in water, e.g. the snail and the whelk, although for ages probably no molluscs were air-breathing land dwellers. In the class of Cephala, to which our snail belongs, there is the sub-class of Gasteropoda, or stomach-footed, because on the ventral side of the body a sole-like disc or foot exists, by the wave-like expansions and contractions of which the animal progresses.

In this sub-class there is a division according to their having or not having an operculum, or means of closing and protecting the orifice of the shell. Most gasteropods which live in water have this; most which live on land (only two exceptions in British molluscs) have not. Here again we must trace our snail down to the sub-order of Pulmonata, or lung or air-sac breathers as distinct from its sisters which inhabit water and breathe by gills. This sub-order is again divided into various families, Arion, Limax, Testacella, Vitrina, Zonites, Helix, etc., and Helix again is divided into various genera, of which Helix is one, and even this is subdivided into sub-genera, Patula, Punctum, Acanthinula, Vallonia, Chilotrema, Gonostoma, Pomatia, Tachea, etc., and to the sub-genus Pomatia our garden snail as well as the "Roman snail" belongs. Looking backwards we, therefore, place our friend as the species aspersa, of the sub-genus Pomatia, of the genus Helix, of the family Helicidæ, of the sub-order Pulmonata, of the order Inoperculata, of the sub-class Gasteropoda, of the class Cephala, of the sub-kingdom of Mollusca, of the kingdom Invertebrata or backboneless animals.

It belongs by origin not to the earliest form of snail, but to the most highly organized group in the world, especially characteristic of the European region, and possessing in their superiority the power to colonize and dispossess the original native snails of other lands. The shell is globular in form with five whorls (the Greek word "helix" means a coil), each usually marked with five bands of pigment. It is mainly a vegetarian, and by habit a lover of the twilight and of moisture. With the exception of H. pomatia it is the largest of our native shells, and is too common to satisfy gardeners. A powerful animal of its kind, it can travel a yard in twelve minutes, or at the rate of a mile in a fortnight, can bear or draw on level ground a weight fifty times its own. It breathes about four times a minute, and its heart-beat varies from sixty to eighty per minute according to temperature, or its activity. It takes its winter rest in clusters, closing its mouth with a membranous film, while if the cold increases it shrinks farther into its shell and makes more epiphragms or film curtains to keep out the cold. Not only on the Continent, but in several parts of England, notably about Bath and Bristol, it is sought, sold, and used for food, and in Belgium it is said to be preferred to the larger and more firm-fleshed H. pomatia. The eggs, from forty to a hundred, are laid in the earth and hatched in from a fortnight to a month, according to the weather. I had observed them as a boy, and used to call tapioca pudding "snail's egg pudding." In the year of their hatching they attain but half their proper size, but after hibernation they eat voraciously and grow rapidly, so as to attain full size in a little more than a year. Most die in their second hibernation (if not destroyed by their many enemies, gardeners, collectors, rats, rabbits, ducks, thrushes, and beetles); but when kept and protected for observation they have achieved the great age of even ten years.

They have a great power of "homing" like pigeons, however far (for them) is their journey after favourite food. The slime-marked journeys or feeding tracks of this species (and still more of slugs) afford matter of great interest. As to sight the two eyes are the dark specks on the tip of the upper pair of "horns," but the range of vision is very short indeed, and the difference between light and approaching darkness is all that some seem able to perceive. The organs of hearing are two small sacs filled with fluid in which are some calcareous grains. They hear little which is audible to human ears, and if not altogether deaf they are dumb as far as we can hear. The power of taste they possess, as is shown by the preference of some foods to others. The sense of touch is acute and resides in all parts of the soft and moist external skin, and especially in the upper tentacles or horns in the Helicidæ. Jaws they have with which to seize and to bite off food, and in H. aspersa and others these bear teeth, but the chief work is done by a sort of toothed tongue, the radula, which rasps off particles of food with a side to side motion of the head as the animal advances. Our aspersa has 12,615 teeth on this ribbon, contained in 145 transverse rows. The organs of digestion are complex and practically much the same as our own. Little vegetation would be left in nature had not, on the one hand, snails been kept down by many enemies as well as by their need of hibernation and their short life; while on the other by numerous devices in the course of ages many plants have protected themselves against the moving machine of a snail's mouth. Cultivated plants, which generally lose their natural protections, have to be guarded by human guards or gardeners. Some plants defend themselves by prickles or hairs, some by hardening themselves with lime or flint, some by bitter or acrid juices. A heart of two chambers, veins, arteries, and blood our snail possesses, and, like man, the old snail has a slower pulse than the young one, and in both exercise increases the pulse rate and also warmth. Breathing is accomplished by a single chamber or air-cell, but also through the skin. As in the case of plants, some kinds are male and female separately, and as some have both powers and products in the same plant, so also is it with mollusca. H. aspersa and most Gasteropoda are of the latter kind.

Having now taken H. aspersa as the representative of our univalves, let us take the "Pearl Mussel"--Unio margaritifer--as that of our bivalves, all of which live in the water, whereas of univalves some are "land snails" and some "water snails." It would say of itself, "I am a species of the genus Unio (unio, a pearl), which belongs to the family Unionidæ, which belongs to the sub-order Isomya (i.e. having muscles of equal power to close the two valves of the shell), which belongs to the order Lamellibranchiata (i.e. having gills arranged in leaf-like fashion), which belongs to the sub-class Pelecypoda (i.e. having a foot somewhat of an axe-shape), which belongs to the class Acephala (headless), which is the second of the two chief classes into which Mollusca are divided.

"I differ from the Gasteropoda (whether they be terrestrial or aquatic) in that I and my near relations are exclusively aquatic and of a sedentary life, which makes the protection of two encompassing shells necessary. These shells are secreted by my mantle lobes, and are united by a ligament which tends to make the valves 'gape' for water and food and by two contracting muscles which close them in danger. I have a degenerate brain and no eyes. My mouth has neither jaw nor teeth, but possesses nervous lips covered with cilia, the vibration of which carries food-laden water to my mouth. My foot, when protruded, is seen as a large muscular appendage, and, by alternately expanding and contracting, it enables me to burrow or plough through mud or even sand, and so disturb the minute organisms on which I feed. I can thus travel fifteen feet a day, or about a mile in a year.

"I have no eyes, but distinguish well between light and shade by means of the surface of my body when exposed. I breathe, that is, get oxygen from the water, by means of gill-plates. As regards other internal organs, I differ not much from H. aspersa, but I am either male or female. Outside I am black and uncomely; but within I am pearly-white, and but for my power of forming pearls round an irritating grain of sand the civilization of England would have come to pass later than it did, for it was the report of my pearls which brought Cæsar to Britain."

* * * * *

Now let us enumerate the species of land and freshwater shells to be found, (all but two) in England, and most of them in Ireland or Scotland.

Arion ater is a large (3 to 5 inches) and common slug, usually black (whence its name ater), but also red, brown, or white. In some varieties the foot-fringe is orange. When irritated it contracts into a hemispherical lump. A few chalky granules under the mantle are the representatives of a shell. See the illustration of three specimens on p. 31. That hole in the mantle is the breathing orifice, and its forward position is a characteristic of the group Arion. The body of slugs is kept moist by a constant exuding of slime from a gland in the tail.