1: A knowledge of this fact was turned to prompt account by Mr. Edgar S. Layard, when holding a judicial office at Point Pedro in 1849. A native who had been defrauded of his land complained before him of his neighbour, who, during his absence, had removed their common landmark by diverting the original watercourse and obliterated its traces by filling it to a level with the rest of the field. Mr. Layard directed a trench to be sunk at the contested spot, and discovering numbers of the Ampullaria, the remains of the eggs, and the living animal which had been buried for months, the evidence was so resistless as to confound the wrongdoer, and terminate the suit.
2: For a similar fact relative to the shells and water beetles in the pools near Rio Janeiro, see DARWIN'S Nat. Journal, ch. v. p. 90. BENSON, in the first vol. of Gleanings of Science, published at Calcutta in 1829, describes a species of Paludina found in pools, which are periodically dried up in the hot season but reappear with the rains, p. 363. And in the Journal of the Asiatic Soc. of Bengal for Sept. 1832, Lieut. HUTTON, in a singularly interesting paper, has followed up the same subject by a narrative of his own observations at Mirzapore, where in June, 1832, after a few heavy showers of rain, which formed pools on the surface of the ground near a mango grove, he saw the Paludinæ issuing from the ground, "pushing aside the moistened earth and coming forth from their retreats; but on the disappearance of the water not one of them was to be seen above ground. Wishing to ascertain what had become of them, he turned up the earth at the base of several trees, and invariably found the shells buried from an inch to two inches below the surface." Lieut. Hutton adds that the Ampullariæ and Planorbes, as well as the Paludinæ, are found in similar situations during the heats of the dry season. The British Pisidea exhibit the same faculty (see a monograph in the Camb. Phil. Trans. vol. iv.). The fact is elsewhere alluded to in the present work of the power possessed by the land leech of Ceylon of retaining vitality even after being parched to hardness during the heat of the rainless season. Vol. I. ch. vii. p. 312.
Dr. John Hunter[1] has advanced the opinion that hybernation, although a result of cold, is not its immediate consequence, but is attributable to that deprivation of food and other essentials which extreme cold occasions, and against the recurrence of which nature makes a timely provision by a suspension of her functions. Excessive heat in the tropics produces an effect upon animals and vegetables analogous to that of excessive cold in northern regions, and hence it is reasonable to suppose that the torpor induced by the one may be but the counterpart of the hybernation which results from the other. The frost which imprisons the alligator in the Mississippi as effectually cuts him off from food and action as the drought which incarcerates the crocodile in the sun-burnt clay of a Ceylon tank. The hedgehog of Europe enters on a period of absolute torpidity as soon as the inclemency of winter deprives it of its ordinary supply of slugs and insects; and the Tenrec[2] of Madagascar, its tropical representative, exhibits the same tendency during the period when excessive heat produces in that climate a like result.
1: HUNTER'S Observations on parts of the Animal Oeconomy, p. 88.
2: Centetes ecaudatus, Illiger.
The descent of the Ampullaria, and other fresh-water molluscs, into the mud of the tank, has its parallel in the conduct of the Bulimi and Helices on land. The European snail, in the beginning of winter, either buries itself in the earth or withdraws to some crevice or overarching stone to await the returning vegetation of spring. So, in the season of intense heat, the Helix Waltoni of Ceylon, and others of the same family, before retiring under cover, close the aperture of their shells with an impervious epiphragm, which effectually protects their moisture and juices from evaporation during the period of their æstivation. The Bulimi of Chili have been found alive in England in a box packed in cotton after an interval of two years, and the animal inhabiting a land-shell from Suez, which was attached to a tablet and deposited in the British Museum in 1846, was found in 1850 to have formed a fresh epiphragm, and on being immersed in tepid water, it emerged from its shell. It became torpid again on the 15th November, 1851, and was found dead and dried up in March, 1852.[1] But the exceptions serve to prove the accuracy of Hunter's opinion almost as strikingly as accordances, since the same genera of animals which hybernate in Europe, where extreme cold disarranges their oeconomy, evince no symptoms of lethargy in the tropics, provided their food be not diminished by the heat. Ants, which are torpid in Europe during winter, work all the year round in India, where sustenance is uniform.[2] The Shrews of Ceylon (Sorex montanus and S. ferrugineus of Kelaart) which, like those at home, subsist upon insects, inhabit a region where the equable temperature admits of the pursuit of their prey at all seasons of the year; and hence, unlike those of Europe, they never hybernate. A similar observation applies to the bats, which are dormant during a northern winter when insects are rare, but never become torpid in any part of the tropics.
1: Annals of Natural History, 1850. See Dr. BAIRD's Account of Helix desertorum; Excelsior, &c., ch. i. p. 345.
2: Colonel SYKES has described in the Entomological Trans. the operations of an ant which laid up a store of hay against the rainy season.
The bear, in like manner, is nowhere deprived of its activity except when the rigour of severe frost cuts off its access to its accustomed food. On the other hand, the tortoise, which immerses itself in indurated mud during the hot months in Venezuela, shows no tendency to torpor in Ceylon, where its food is permanent; and yet is subject to hybernation when carried to the colder regions of Europe.
To the fish in the detached tanks and pools when the heat, by exhausting the water, deprives them at once of motion and sustenance, the practical effect must be the same as when the frost of a northern winter encases them in ice. Nor is it difficult to believe that they can successfully undergo the one crisis when we know beyond question that they may survive the other.[1]