Imatges de pÓgina

with its slime a fine membrane, interposed between the mantle and extraneous substances. Soon afterwards the mantle secretes a large portion of very white fluid over its whole surface, which instantly sets uniformly, and forms a kind of solid operculum like plaster of Paris, about half a line in thickness, which accurately closes the mouth. When this is become hard the animal separates the mantle from it. After a time, expelling a portion of the air it had inspired, and thus being reduced in bulk, it retreats a little farther into the shell, and forms another leaf of mucus, and continues repeating this operation till there are sometimes five or six of these leaves forming cells filled with air between it and the operculum.

The membranous partitions are more numerous at the end than at the beginning of winter, and, in snails inhabiting the mountains, than in those on the plains. These animals hybernate at the proper period, at very different temperatures, varying from 37° to 77° Fahrenheit. Respiration ceases during the period of hybernation.

The mode in which these animals escape from their winter confinement is singular: the air they had expired on retiring into their shell farther and farther, remains between the different partitions of mucus membrane above mentioned, which forms so many cells hermetically sealed; this they again inspire, and thus acquiring fresh vigour, each separate partition, as they proceed, is broken by the pressure of the foot, projected in part through the mantle; when arrived at the operculum they burst it by a strong effort, and finally detaching it, then emerge, begin to walk and to break their long fast.

In all these proceedings the superintending care and wise provisions of a Father Being are evident. This creature can neither foresee the degree of cold to which it may be exposed in its state of hybernation, nor know by what means it may secure itself from the fatal effects it would produce upon it, if not provided against. But at a destined period, often when the range of the thermometer is high, not stimulated by a cold atmosphere, except, perhaps, by the increasing length of the night, at the bidding of some secret power, it sets about erecting its winter dwelling, and employing its foot both as a shovel to make its mortar, as a hod to transport it, and a trowel to spread it duly and evenly, at length finishes and covers in its snug and warm retreat; and then, still farther to secure itself from the action of the atmosphere, with the slimy secretion with which its Maker has gifted it, fixes partition after parti

1 Gaspard and Bell, Zool. Jour. i. 93.—ii. 174.

tion, and fills each cell formed by it, with air, till it has re treated as far as it can from every closed orifice of its shelland thus barricades itself against a frozen death. Again, in the spring, when the word is spoken-awake, thou that sleepest -it begins immediately to act with energy, it reinspires, as above related, the air stored in its cells, bursts all its cerements, returns to its summer haunts, and again lays waste our gardens.

We may observe here, with respect to this, and all hybernating animals, a beautiful relation and correspondence between their habits and their functions. Their official duty is to remove superfluities and nuisances, to prevent vegetable substances from encroaching too much upon each other, to remove entirely those that are dead and putrescent. At the season of the year, therefore, when the former are in full vigour, forth issue from their various retreats the innumerable tribes that make them their food, but when they cease to grow and flourish these services are not wanted, and the animals who perform them disappear from the face of nature. Again, when dead animals, or the excrements of living ones, or the sweets issuing from innumerable flowers, would clog the air that we breathe with effluvia unfriendly to health and life-countless armies are every where upon the wing, or on the alert, to prey upon such substances, and prevent their miasmata from breeding a pestilence amongst us; but when the cold season returns, the flowers lose their leaves and blossoms, and exhale no longer their sweets, and the scents arising from putrescent and other fœtid substances become no longer annoying. Then the whole army employed in this department disappears, and the face of nature seems to lose the most busy part of its popula tion, gone to a long repose.

It is worthy of remark, with respect to the terrestrial animals of the tribe we are considering, that they all delight in shady and moist places, and that during hot and dry weather they seldom make their appearance, but no sooner comes a shower, than they are all in motion. It is probable that their power of motion is impeded by a dry soil, and that the grains of earth and small stones, when quite dry, adhere to their slimy foot.

As many of the marine shells appear in some degree amphibious, for instance, the Chitons and the Limpets, so, perhaps, some of the terrestrial ones may occasionally enter fresh waters; indeed the amber shells,' at least one species,2 is stated

1 Succinea.

2 S. elongata.

'to swim occasionally on the surface of the water. From these circumstances it scems not improbable that the shell-fish, as well as the birds, so vast a proportion of them being marine animals, were all amongst the objects created on the fifth day, and produced by the waters.

There are very large and beautiful shells found in South America, belonging to the terrestrial herbivorous section and to different genera1 divided from Helix of Linné, but we know nothing of their history or habits: I shall therefore now say something upon the marine herbivorous Trachelipods.

The violet snail, which, according to the account of its manners given by Bosc, who paid particular attention to then in a voyage from France to America, exhibits several very remarkable peculiarities. When the sea is calm, these animals may be seen collected often in large bands, swimming over the surface by means of a floating apparatus consisting of aerial vesicles, produced by their foot: and attached to its posterior part, a little below the point to which the operculum is fixed in other genera, and to which Cuvier thinks it bears some analogy, who also observes that has a natatory membrane or fin on each side of its body. During this action their head is very prominent, and the foot is so extended that the float or line of vesicles forms an angle with the middle of the shell. When the sea is rough, the animal absorbs the air from its vesicles, changes the direction of its foot, contracts its body, and lets itself sink. It does the same when in danger from any enemy, and farther, like the cuttle-fish and some others, colours the water by the emission of a blue fluid, which serves to conceal it. They are vividly phosphoric in the night. Birds carry them off with great dexterity.

If their floating apparatus is mutilated, the foot can reproduce it. The latter is flat towards the head, this part of it is furnished with a transparent membrane, which extends far beyond its extremity, and is composed of a large number of vesicles of unequal size, those in the middle being the largest; these vesicles the animals fill with air at their pleasure. The violet-coloured shell of this little animal is remarkably thin, which facilitates its excursions on the surface. It is singu'ar that under this fragile vesicular float, a little line of pearly fibres may be perceived, to which are attached its eggs; in some species they are contained in little membranous bags or sacs. It is thought that the young animals, when liberated

1 For instance, Achatina Bulimus, &c. 2 Janthina, PLATE VI. FIG. 2.

3 PLATE VI. Fro, 2. a.

from these bags or chambers, ascend their mother's float, and so are transported to the surface. Fishes are enabled to rise to the surface of the water by means of their air-bladders, and some radiaries by a vesicle which surmounts them,' but neither of them are more singular than these outriggers by which the vessel of the violet-snail is kept both buoyant and steady.

The foot of the Molluscans, when we first observe it, seems to us merely an organ of locomotion, nothing remarkable in its structure, and incapable of any multifarious action, but when we study the history of this and the preceding snail, we see that it is a most important organ, and which performs a greater variety of operations than almost any organ of any other animal. We have seen that it spins a fine silk and thread; that it secretes a fluid serviceable for several purposes: that it can form a float, as in the present instance; that it can be used as a hand in excavating and building, and various other manipulations, so that in giving them this instrument and endowing it with such a variety of functions in the various tribes, their Creator gave them every thing they wanted.

Perhaps the followers of Lamarck may say that, in the present instance, the animal constructs its own float itself, at the impulse of its own wants. But uninstructed by its Creator, how could it learn that vesicles full of air would serve to float its little boat, and if not already organized to answer the impulse of an exciting cause, in vain would the will of the animal, if so instructed, endeavour to produce and inflate the vesicles, or, when it willed to sink, to empty them of air.

The shell-fish of the aquatic tribe best known in this country is the periwinkle, vulgarly called the pin-patch, which next to the oyster and the cockle, seems most in request as a relishing article of food. These animals, as I observed, not very long since at Cromer, in Norfolk, appear to make the bladder-kelp, which, at low water, may be seen there in large patches, a kind of submarine pasture, for I found them in abundance upon it at low water. As the Creator willed that the waters, whether salt or fresh, should have their peculiar inhabitants, it was requisite that each should have its appropriate food. Did all feed upon the same substance there would be a universal struggle, unless, indeed, the entire variety of the submarine botanical world was done away, and one homogeneous article provided, in such quantity as to be a sufficient supply for all. But farther, doubtless, different organizations and forms could not be maintained upon the same pabulum, and therefore dif

1 See above, p. 104. 2 Turbo litoreus.

3 Fucus vesiculosus.

ferent creatures required different articles of food, or different parts of the same article. Here was a mutual office-the numberless vegetable productions require to be kept within due limits, and therefore the functions of the aquatic animals is to maintain them in due relative proportions. Was the ocean and all its streams planted as now, and there were no animals of any description to keep in check its vegetable productions, they would all in time grow up and choke the rivers and gradually raise the bed of the ocean till there would be no

more sea.

1 Cypræa.

4 Buccinum.
7 Cassis.

10 M. Tribulus.

Having considered the plant-devouring Trachelipods, I shall say something next upon the carnivorous or predaccous ones, which form the great body of large marine shells, and those which most ornament our cabinets, for to this tribe belong the Cowries, Cones,2 Mitres, Whelks, Tuns, Volutes," Helmets," Rock-shells, Strombs, and other conchs which exceed the general run of shells in beauty, form, and magnitude. But with regard to their habits and instincts we know little or nothing of any interest.

They are distinguished from the herbivorous ones by breathing the sea-water, for they are all submarine, by means of a siphon or tube, instead of by an aperture in the neck; in the place of maxillæ, their mouth is furnished with a retractile proboscis, with which they pierce and suck other shell-fish. The aperture of the shell is also very different, the siphon being accompanied sometimes by a channel, and sometimes by a notch at the base of the aperture.

The tribe most celebrated from ancient times, on account of the vaunted purple dye which one species produced, is that constituted by the Rock-shells, or Linné's great genus, Murex, and Lamarck's canaliferous Zoophagans, called so from the long straight canal which terminates the mouth of their shells. The principal feature of this tribe, besides their long channelled beak, is the vast variety of spines, and other processes and ridges, with which their Creator has armed a great number of them; the beak and mouth of several give them no small resemblance to the heads of certain birds, thus one is called the thorny woodcock,10 another the suipe," &c.

At the first blush, an inquirer into the use of these spines

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