LITMIR.BIZ

      GARDEN SNAIL.

      Many terrestrial Mollusca which ordinarily inhabit moist places, are enabled, by a precaution similar to that adopted by our own Snail in ​drought, to sustain life, in such a state of retirement and suspension of their usual habits, not for a few days or weeks only, but even for many years. Numerous examples have occurred in which the land-shells of distant countries have been brought to England, alive but torpid, and have been kept shut up in drawers for twelve, eighteen, and even twenty months; manifesting no signs of life until moistened, when they presently crawled about, and began to eat. But the most singular example of this protracted sleep on record, is that of Mr. Simon's Snails, which must surely have been the veriest Rip Van Winkles among Mollusca. The following account is from the Philosophical Transactions; and the facts seem to have been carefully investigated, and well authenticated:—

"Mr. Stuckey Simon, a merchant of Dublin, whose father, a fellow of the Royal Society, and a lover of natural history, left to him a small collection of fossils and other curiosities, had among them the shells of some snails. About fifteen years after his father's death (in whose possession they continued many years), he by chance gave to his son, a child about ten years old, some of these snail-shells to play with. The boy put them into a flower-pot, which he filled with water, and the next day into a basin. Having occasion to use this, Mr. Simon observed that the animals had come out of their shells. He examined the child, who assured him that they were the same he had given him, and said he had also a few more, which he brought. Mr. Simon put one of these into water, and in an hour and a half after, observed, that it had put out its horns and body, which it moved but slowly, probably from weakness. Major ​Vallancy and Dr. Span were afterwards present, and saw one of the snails crawl out, the others being dead, most probably from their having remained some days in the water. Dr. Quin and Dr. Rutty also examined the living snail several different times, and were greatly pleased to see him come out of his solitary habitation after so many years' confinement. Dr. Macbride and a party of gentlemen at his house, were also witnesses of this surprising phenomenon. Dr. Macbride has thus mentioned the circumstance:—'After the shell had lain ten minutes in a glass of water that had the cold barely taken off, the snail began to appear, and in five minutes more we perceived half the body pushed out from the cavity of the shell. We then removed it into a basin, that the snail might have more scope than it had in the glass; and here, in a very short time, we saw it get above the surface of the water, and crawl up towards the edge of the basin. While it was thus moving about, with its horns erect, a fly chanced to be hovering near, and, perceiving the snail, darted down upon it. The little animal instantly withdrew itself into the shell, but as quickly came forth again, when it found the enemy had gone off. We allowed it to wander about the basin for upwards of an hour, when we returned it into a wide-mouthed phial, where Mr. Simon had lately been used to keep it. He presented me with this remarkable shell, and I observed, at twelve o'clock, as I was going to bed, that the snail was still in motion; but next morning I found it in a torpid state, sticking to the side of the glass."^[10]

      ​In treating of the food of the Mollusca, Dr. Johnston divides them into three classes; first, those which take their food in a liquid form, or suspended in water; secondly, those which are more properly carnivorous; and, thirdly, those which feed on vegetable matter.

      Under the first division are comprised all those which have no distinct head, including the three classes, Tunicata, Brachiopoda and Conchifera. None of these have any power of pursuing prey, nor any organs for mastication. Yet any one who has ever examined with a microscope, either the sea-water, which appears to the naked eye pure and simple, or the impalpable sediment which lies upon the bottom, will be at no loss to discover abundant organic matter fitted to supply nutriment to these headless, generally stationary, and apparently helpless creatures. Countless millions of Infusorial animalcules sport in the clear water, altogether unappreciable by our senses, while vegetables clothed with flinty shells, the Diatomaceæœ of botanists, equally numerous and equally minute, crowd the mud on the floor of the sea.

      In order that these minute bodies should afford nutriment to the headless Mollusca, a simple but effective contrivance is provided. The currents which ceaselessly play over the breathing organs, produced by the cilia which cover them, not only bring water to be respired, but come charged with the various organic particles, both animal and vegetable, that occur in the vicinity. It is, therefore, merely necessary that the orifice of the stomach, which for convenience sake may be called the mouth, be situated in the course of the currents, and be endowed with the power of ​selecting and retaining such substances as are suitable for digestion.

      The remaining classes divide themselves into flesh-eaters, and those which live upon vegetable diet, the preponderance, however, being, as well as can be estimated, rather with the former. Not a few of the Univalves feed upon their Bivalve relatives, not seizing the opportunity, as has been pretended, of killing their victim as it lies incautiously with gaping shells; but by drilling a small hole through one of the valves, and extracting the fleshy parts, particle by particle. Some species devour dead fishes and other putrifying animal matters with avidity. Many of the elegant naked-gilled tribes prey on each other, though their proper food consists of zoophytes. I have found the large Eolis papillosa tear away the tentacles of different species of sea-anemones, which seemed to be its natural food.

      The Cephalopoda, including the Cuttles, the Poulpes, and the Squids, are fierce and predatory, the tyrants of the deep. Furnished with many long arms, stretching in all directions, and studded with rows of adhesive suckers, they seize with ruthless grasp any passing fish or other animal, whose strength is inferior to their own, and drag it to a hard and sharp horny beak, the mandibles of which resemble those of a parrot's bill, and being moved by powerful muscles are enabled either to crush the shells in which their victim may be enclosed, or to tear it to pieces if it be a fish, or other animal of muscular or sinewy tissues.

      In speaking of the vegetable-feeding Mollusca, the ravages committed by those pests of our gardens, the Slug and Snail, will occur to every one. Other ​species of the same genera are never or rarely seen in gardens, but devour the herbage of the roadside, the bank, or the hedge. Many, particularly those which inhabit the woods of foreign countries, devour the leaves of trees. The plant-eaters among the marine tribes live upon the various kinds of sea-weeds, of which there is a sufficient variety to gratify a taste much more epicurean than it probably is in reality. The common Periwinkle and the Limpet are both vegetable feeders, and there is a pretty little species of the latter genus which invariably, I believe, confines itself to one plant: this is the Patella pellucida, distinguished by having on its summit three or four lines of blue, most brilliantly gemmeous. It feeds on the tangle, (Lammaria digitata) eating away a cavity for itself, just large enough to contain its body, in the substance of the cartilaginous stem, commonly beneath the shelter of the arching roots. I have pulled up the tangles by dozens at low spring-tide, and have scarcely ever found one that had attained certain dimensions without finding a little parasitical Limpet embedded in its substance.

      If we measure the interest which we take in any section of created beings by their powers of conferring benefit or inflicting injury on our own race, we shall find the Mollusca not unworthy of our regard in both these respects. Many of them are used as human food, and that not by savage nations only, but by ourselves and by all classes of society. The Limpet, the Periwinkle, the Whelk, the Mussel, and the Cockle, are commonly sold in the streets of our sea-port towns and large cities, though these are certainly more prized by the lower classes of society than by those of more cultivated tastes. ​There is no doubt that many if not all of our larger Bivalves might be added to the list, and probably some of these might prove not unworthy of a place among more delicate viands. I have myself tried the large Pholas dactylus, that bores the sandstone, and have found its substance tender, and its taste agreeable.

Скачать книгу