The purpose of the respiratory organs, and of the currents just described, is, to expose the blood freely to the purificative action of the atmospherical air, that it may be purged of some noxious qualities which it has acquired during its circulation through the venous system, and fitted again for the continuance of the life of the individual. In the vertebrate animals the blood is altered, even in its outward appearance, by this process; from a dark it becomes a bright red fluid: but no perceptible change is operated on the white serous blood of the Mollúsca, yet that it has experienced a similar purification is not to be doubted; for the air breathed by these creatures is similarly deteriorated, as it would have been had it been breathed by the quadruped or bird; the oxygen has disappeared, and its place become occupied by an equal bulk of carbonic acid gas. This had been proved by the well known experiments of Spallanzani and other physiologists; and though, in general, the proportion holds good, yet it appears, from the recent experiments of Treviranus, that the absorption of oxygen is not always proportional to the excretion of carbonic acid, the proportion of the one to the other depending on the strength of the respiration, the time of its continuance while the respirability of the air is diminishing, and the volume of the air in which the respiration is performed. "The more carbonic acid," says Treviranus, "there is developed while breathing in the open air, and the less the power of continuing in a medium deficient in oxygen, the less is the proportion of the consumption of oxygen to the production of carbonic acid gas, whence a small quantity of atmospheric air is respired for a moderate period. But when the respiration is continued for a longer period in the same air, and the strength of the individual begins to sink, the excretion of the latter diminishes more rapidly than the absorption of the former. We know that the higher classes of animals, when enclosed in a certain quantity of air, die long before all its oxygen has been exhausted. The case is very different with many of the Mollúsca under the same circumstances; for they not only consume all the oxygen, but actually continue afterwards to exspire carbonic acid gas: consequently, after the respiration has been continued for some time, there has been more of the latter excreted than there has been consumed of the former; nay, sometimes this occurs even before all the oxygen has been consumed." (Edin. New Phil. Journ., April, 1833, p. 383.*) These observations may serve to

The Rev. Mr. Guilding has conjectured that some Mollúsca may even purify water:-" Neritinæ are destroyed with great difficulty: some,

:

explain, in some degree, the apparent apathy of the Mollúsca generally to a temporary deprivation of their respiratory media for snails may be immersed in water for many hours without injury; and the purely aquatic species will survive as long a time exposed to the atmosphere. Oysters and muscles, as every one knows, and probably all the Conchífera, will live for three or four days without any more water to breathe in than what may lie in the concavity of their shells; and Mr. Boyle has some experiments which illustrate, in a remarkable manner, their tenacity of life even in vacuum. He found that two oysters, put "into a very small receiver," exhausted of air, were alive at the end of twenty-four hours; "but how long afterwards they continued so, I did not observe." (Phil. Trans., 1670, p. 2023.) Another oyster was put into a vial full of water before being enclosed in the receiver, “that, through the liquor, the motion of the (air) bubbles, expected from the fish, might be more pleasantly seen and considered. This oyster proved so strong, as to keep itself close shut, and repressed the eruption of the bubbles, that in the other did force open the shells from time to time; and kept in its own air as long as we had occasion to continue the trials.” (Ibid., p. 2024.) Shelled snails (Hélices) appeared to be not more disordered in vacuity; and even the slugs (Lìmax) endured the privation for many hours. The same illustrious philosopher included two of the latter "in a small portable receiver," carefully exhausted; but, though they did not lose their motion near so soon as other animals were in our vacuum wont to do, yet, coming to look on them after some hours, they appeared moveless and very tumid; and, at the end of twelve hours, the inward parts of their bodies seemed to be almost vanished, and they seemed to be but a couple of small full-blown bladders; and, on the letting in of the air, they immediately so shrunk, as if the bladders had been pricked: the receding air had left behind it nothing but skins; nor did either of the snails afterwards, though kept many hours, give any signs of life." (Ibid., p. 2050.) In this experiment, it is obvious that the snails were killed from the mechanical effects of the expansion of the air within them, and not from its ingress to the pulmonary cavity being prevented.

66

which were even kept close in salt water, seemed to have the power of purifying it, and rendering it fit for respiration; while many large airbubbles were generated in the glass. Some power of this kind would be very valuable to those species which inhabit maritime ponds, the waters of which, nearly dried up at certain seasons, must be stagnant and unwholesome." (Zoological Journal, vol. v. p. 33.)

But there are on record some extraordinary facts, which seem to prove that, under certain conditions, all of which are not yet known, the respiration of many Mollúsca, more especially the terrestrial, may be suspended for an indefinite period, and again renewed by the application of heat and moisture; life, as it were, keeping watch, and holding at bay every destructive agent, but without giving any outward sign of her presence and constant wakefulness, until the return of those influences in which she joys. "All the land Testàcea," to use the words of Dr. Fleming, "appear to have the power of becoming torpid at pleasure, and independent of any alterations of temperature. Thus, even in midsummer, if we place in a box specimens of the Hèlix hortensis, nemoralis, or arbustòrum, without food, in a day or two they form for themselves a thin operculum, attach themselves to the side of the box, and remain in this dormant state. They may be kept in this condition for several years. No ordinary change of temperature produces any effect upon them, but they speedily revive if plunged in water. Even in their natural

haunts, they are often found in this state during the summer season, when there is a continued drought. With the first shower, however, they recover, and move about; and at this time the conchologist ought to be on the alert." (Phil. Zool., vol. ii. p. 77.) I may illustrate these remarks, which are perfectly correct, by some additional examples; one or two of which you may find to require an exercise of faith for which you may not be altogether prepared. Mr. Lyell tells us that "four individuals of a large species of Bùlimus, from Valparaiso, were brought to England by Lieutenant Graves, who accompanied Captain King in his late expedition to the Straits of Magellan. They had been packed up in a box, and enveloped in cotton, two for a space of thirteen, one for seventeen, and a fourth for upwards of twenty months; but, on being exposed, by Mr. Broderip, to the warmth of a fire in London, and provided with tepid water and leaves, they revived, and are now living in Mr. Loddiges's palm-house." (Princ. Geol., vol. ii. p. 109.) Dr. Elliotson put a garden snail into a dry closet, without food, a year and a half ago: it became torpid, and has remained so ever since, except whenever I have chosen to moisten it. A few drops of water revive it at any time." (Blumenbach's Physiology, p. 182.) Similar instances may be found in some of the periodical journals; but they are as nothing when compared with the snails of Mr. Stuckey Simon, a merchant of Dublin, which, on being immersed in water, recovered and crept about after an uninterVOL. VII.- No. 38.

rupted torpidity of at least fifteen years; and I agree with Mr. Bingley in thinking that this is a well-authenticated fact. Whether what follows is so, I leave to your own decision ; but I will not say you are unreasonably sceptical if you deem it too tramontane. "Professor Eaton of New York stated," says my authority," that the diluvial deposits through which the Erie Canal was made contained ridges of hard compact gravel. On cutting through one of these, near Rome village,

"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 Vallancey 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 about 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 was gone off. We allowed it to wander about the basin for upwards of an hour, when we returned it into a wide-mouthed phial, wherein Mr. Simon had lately been used to keep it. He was so obliging as to present 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.'

"A few weeks afterwards the shell was sent to Sir John Pringle, who showed it at a meeting of the Royal Society; but some of the members imagining that Mr. Simon must have been imposed upon by his son having substituted fresh shells for those that had been given to him, the boy was reexamined by Dr. Macbride on the subject, who declared that he could find no reason to believe that the child either did or could impose upon his father. Mr. Simon's living in the heart of the city rendered it almost impossible for the boy (if he had been so disposed) to collect fresh shells, being at that time confined to the house with a cold. Mr. Simon has also declared that he is positive those were the shells he gave to him, having in his cabinet many more of the same sort, and nearly of the same size." (Bingley's Animal Biography, vol. iii. p. 574.)

16 miles west of Utica, the workmen found several hundred of live molluscous animals. They were chiefly of the Mỳa cariòsa and Mya purpurea. The workmen took the animals, fried, and ate them. He adds, 'I was assured that they were taken alive 42 ft. deep in the deposit. Several of the shells are now before me. The deposit is diluvial. These animals must have been there from the time of the deluge, for the earth in which they were is too compact for them to have been produced by a succession of generations. These freshwater clams of 3000 years old precisely resemble the same species which now inhabit the fresh waters of that district; therefore, the lives of these animals have been greatly prolonged by their exclusion from air and light for more than 3000 years.' (Silliman's Amer. Journal, No. xv. p. 249., as quoted in Turner's Sacred History, p. 473.)

With the exception of the last example, the others refer to land Testàcea; but some pulmoniferous aquatic species are equally capable of assuming this state of torpidity, when under circumstances which deprive them of their respiratory medium. In early spring, I have more than once observed the Limnèus fossàrius to abound in small pools of water, which were dried up as the season advanced; and when, after a careful search, the little snails were found, in a torpid condition, concealed in the cracks made by the drought, or under small clods of earth, where they awaited a happier season to refill their pools, and permit them to resume the functions of active life. Perhaps, in this country, their torpidity can rarely be continued beyond a few weeks; but, in tropical climes, similar species can pass the dry season of five long months in this state. Thus, Adanson informs us that the minute freshwater shell, which he calls Bùlimus, is to be seen only from the month of September to January, in the marshes of Senegal, formed by the rains which fall in June, July, August, and September. When these marshes are dried up, and, as it were, roasted by the sun, the shellfish disappear; a few empty shells alone being left, to show where they had been; but they never fail to return with the rainy season; and Adanson remarked that, the hotter the preceding summer, the more abundant was the issue of the succeeding hordes. How, asks the author, shall we explain this marvellous reproduction? Can the eggs of the animal, necessarily very delicate and minute; can they remain in a soil so burned up, without being entirely dried; or can the animals themselves, if it is true that they conceal themselves in the bosom of the earth, can they resist, during five or six months, the heat of a burning sun? (Hist. Nat.