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themselves from the cold and storms of the season, yet I have always found them immediately to resume their activity when taken from their concealments, and they are in motion all the winter in mild weather. It is not certainly known, although the contrary has been asserted *, that any marine Molláscum hybernates. There would seem to be no necessity that the snails of tropical countries should be endowed with this remarkable property; but the observations of Adanson prove the contrary. He tells us that the Búlimus Kámbeul apparently passes the winter, or dry season, in a deep slumber, like the snails of Europe; for he found several of them which were half-buried, in the month of September, at the roots of trees and in the thickest brushwoods; and of these some had already closed the aperture of their shell very exactly with a lid of a whitish and plaster-like matter, to protect themselves against the long droughts which continue for eight or nine months uninterruptedly. (Hist. Nat. du Sénégal, p. 18.) None of the hybernating Mollásca exhibit any remarkable cunning in the selection of their hybernacula or winter quarters. On the approach of the cold weather, the terrestrial tribes seek out a convenient station in crevices of old walls, at the roots of coarse grass, or in tufts of moss, and, retiring within the shell, they close up its aperture by a membranous or calcareous epiphragm, which serves, at the same time, to fix or cement the shell to the wall or body against which it rests. At the same period, the aquatic tribes descend to the bottom of their ponds and ditches, sink a little in the soft mud, and cover over the mouth of the shell with a transparent gelatine. In general, when the temperature of the air sinks below the 50th degree of Fahrenheit, cold-blooded animals begin their winter slumber, and, previously prepared by that instinct which operates as wisely as if right reason had foreseen the coming evil, they gradually, with the increasing cold, sink into a state which resembles more the stillness of death than the quietness of sleep; a state without motion, or feeling, or sense, or heat, and in which the heart and lungs, the vital organs, perform their functions more and more j 3. until they also rest still in the general quiescence; and in this deathlike condition these animals continue “for five, six, seven, or even eight or nine months, according to the climate and season,” until the genial warmth and dews of spring recall them anew to life and action. M. Gaspard has given a minute and a very interesting
* “The marine Mollásca probably migrate in part from the shallower to the deeper waters in cold winters: many, however, hybernate.” (Duncan on the Analogies of Organised Beings, p. 97.)
account of the hybernation of Helix pomatia, in the first volume of the ooological Journal; to which I must refer you for the particulars. This species forms, by aid of its foot and a very glutinous secretion, an excavation or nest, in which it buries the shell, and it then closes the aperture with a thick calcareous epiphragm, and with several interior membranous partitions, which are more numerous at the end than at the beginning of winter, and in the snails inhabiting the mountains than in those found on low ground. Thus buried and enclosed, it passes six months in a state of total torpidity; for the only indication of irritability perceptible during this period is a slight contraction of the collar of the mantle when touched, on removing the epiphragm. He found that there was no digestion; the heart at first beat feebly, and with a very slow pulsation; but at a later period it was found to have stopped, and the circulation was entirely suspended; respiration ceased; no animal heat, which even in the summer, when respiration and circulation are most lively, does not exceed one degree above the surrounding atmosphere, was evolved; no secretions nor wasting function went on, neither any growth or reproduction of new parts. “In our climate, it is about the beginning of April, soon after the song of the cuckoo begins and the swallows appear, that the snails leave their torpid state; varying a little, however, according to the season. The mode by which their escape from confinement is effected is simple and easily comprehended. The air which is contained in the different cells, and which had been expired on the animal withdrawing itself farther and farther into the shell after the formation of the operculum, is again inspired, and each separate membranous partition broken by the pressure of the hinder part of the foot projected through the mantle. When it arrives at the calcareous operculum, the animal, making a last effort, bursts and detaches its most obtuse angle. Then insinuating by little and little the edge of the foot between the shell and the operculum, it forces the latter off, or breaks it away. The animal then comes forth, walks, and immediately begins feeding, with an appetite excited, doubtless, by an abstinence of six or seven months.” (p. 99.) Such is M. Gaspard's account of the reviviscency of Hélix pomătia, and the process must be still simpler in the other species; for they have merely to rupture a single horny or semigelatinous membrane. But there has been a difference of opinion relative to the source of the air which is first respired. Gaspard, you will observe, says that that portion which is confined between the layers of the epiphragms is
the first inhaled ; and, in coincidence with this opinion, we must infer that the species with a single membrane respire in the first instance the air behind it, and then, by their own efforts, burst their prison wall. A very different explanation of the process has been advanced by Sir Everard Home. He says :—“ When warmth and moisture are applied, the membranous film (of the garden snail) falls off; a globule of air that remained in the cavity of the lungs becomes rarefied, and forces its way out, and admits of fresh air being applied to these organs.” * (Comp. Anat., vol. iii. p. 156.) I suspect that more of fancy than of observation enters into the baronet's theory; for were the rarefaction of the contained air, and its egress through the pulmonary aperture, all that was necessary to shake off the winter slumber, this would be done on several days in winter and in early spring, when the sun shines brightly and the atmospherical temperature is high enough to produce the effect, often higher, indeed, than it is when they begin, in the appointed time, to leave their hybernating retreats. If, says M. Gaspard, individuals of Hèlix pomàtia “ were exposed during the winter to a dry heat of from 60° to 100° for several days, or even weeks, not one made its appearance; whilst, on the contrary, those which were placed in a deep recess, the regular temperature of which was 50°, came forth in April, or at the beginning of May, without any increase of temperature.”
Dr. Turton, on the other hand, maintains that the doctrine of Gaspard is equally untenable; for that the direct communication between the external air and the animal within its shell is never interrupted, but on the contrary preserved, by means of a small aperture in the epiphragm. His words are:-“ But, upon examination, it will appear, that in the
* In the following extract Sir E. Home repeats his hypothesis in a more detailed manner:-" It is curious that, although respiration is necessary for carrying on the functions of life, it is by no means so for the continuance of its existence. The garden snail illustrates this fact in the most satisfactory manner. When the temperature of the atmosphere sinks below a certain degree, this animal places itself upon a solid body, that it may not be liable to fall off: it then forms an operculum of mucus, by which respiration is stopped, and the animal remains hermetically sealed up till warmth and moisture dissolve the mucus by which the animal was fixed to its place; and a globule of air retained in the lungs, which consist only of one cell or bag, being rarefied, escapes externally, restoring the communication with the air of the atmosphere which rushes in, and the action of the heart is renewed. If it is admitted that the application of oxygen to the muscles of the heart is capable of stimulating that organ, nothing can be more simple than the mode in which this is effected : the oxygen of the atmosphere is absorbed by the blood in the lungs, and the closeness of the ventricle of the heart to the lungs permits the oxygen to penetrate to the heart.” (Comp. Anat., vol. v. p. 129.)
centre of this epiphragm (of Hélix pomatia) is an exceedingl minute orifice, communicating with an umbilical cord, . is connected with a fine placenta-like tissue of vessels, penetrating into the pulmonary cavity itself; and this minute orifice, although not large enough to admit a drop of water, is of sufficient capacity for the passage of that quantity of oxygenated air necessary for the purposes of extremely slow, but not totally extinct, respiration. If this orifice be covered over with a coat of wax or varnish, so that all possible connection with external air be excluded, animal life becomes altogether extinguished, never to be again restored. We have observed this minute puncture in the winter covering of the H. ericetorum and some others; and it is probable that all whose aperture is closed during the cold season only, are furnished with this beautiful apparatus for the preservation of life.” (Manual of Land and Freshwater Shells, p. 46.) I recommend you to examine into those very interesting statements; and, if your own observations confirm them, they will materially alter some inferences which have been drawn from Gaspard's experiments, and adopted by us, in reference to the total cessation of the action of the lungs and heart. That snail does not reach this northern latitude; but I have examined, too carelessly however, the epiphragm of Hélix aspérsa during its hybernation, and always find a small aperture in it; and also, in the aquatic tribes, } find a larger hole in their thin winter operculum, intended, assuredly, to keep up the communication between the pulmonary cavity and circumambient medium in their season of repose.
There is something admirable in this curious adaptation of the economy of the hybernating creatures to their situations; for otherwise they could not live beyond a single summer in the countries which they now inhabit with impunity to themselves. If, during their active state of existence, you were to keep a Limněus, or any other aquatic pulmoniferous species, immersed in water for only one short day, it would die irrecoverably; but it remains under water, perhaps with the surface frozen over, for three or four months uninjured, when the system has been prepared, in autumn, for the change. And so of the land kinds: they perish if deprived of air for a few hours only in summer, or if exposed to an artificial cold not lower than the cold of winter; but in a state of hybernation they respire, if any, such a small quantity of air as is not to be appreciated, and brave our longest and severest frosts without peril and without pain. “O Lord, how glorious are thy works thy thoughts are very deep !”
Sept. 26. 1833. G. J.
ART. IV. On Structure, and its adaptedness to Economy in the Annulate Animals. By 0.
The most advantageous occupation for man is the study of the works of his Creator; this study is also the most natural, and consequently the most gratifying. Man delights to enquire into the means employed to accomplish appointed ends; he possesses an innate desire to discover the causes of those obvious phenomena which are continually attracting his attention. It is but too frequently the aim of those who instruct youth to repress this desire, this thirst for natural knowledge, supposing it likely, if encouraged, to interfere, in after-life, with the pursuit of power and riches, which are generally the only desiderata held up to our youthful hopes. It should be far otherwise; the expanding mind, like the growing body, should be copiously supplied with wholesome nutriment, else its tastes become vitiated and its power weakened. There is nothing which enables an ardent and aspiring mind to form so just an estimate of itself, as does an idea, however imperfect, of something greatly superior. Now, that mind must be lost to the power of thinking, that cannot trace in the circulation of the blood, in the conversion of an egg to a chicken, or in the reproduction of a spider's leg or a lobster's claw, the design and superintendence of an intelligence infinitely above its own. Let man enquire into these things. As he imbibes great and important truths in natural history, he becomes deeply imbued with a sense of his own insignificance. His first safe step in knowledge is the assured feeling of his own utter ignorance.
I have long desired the opportunity now afforded me, of addressing readers among whom many will be willing to consider themselves learners. For the learned I have no novelties in store. I address myself more particularly to those yet in the morning of life, whose enthusiasm of enquiry has received no chill from the unsatisfactory sophisms and pedantry of some of the self-elected dictators in natural history. I am no dictator, but a fellow enquirer: my solicitation is, “Come with me, a lowly and unworthy son of science; come with me, and let us together meditate on the wonderful works of our Creator. Let us examine together the structure of one branch of the animal kingdom. Let us trace the peculiarities which distinguish it from the other branches. Let us see how beautifully these very peculiarities are adapted to the parts in the creation which these creatures are designed to perform.”