Being desirous of obtaining a specimen of fish so exhumed, I received from the Moodliar of Matura, A.B. Wickremeratne, a fish taken along with others of the same kind from a tank in which the water had dried up; it was found at a depth of a foot and a half where the mud was still moist, whilst the surface was dry and hard. The fish which the moodliar sent to me is an Anabas, closely resembling the Perca scandens of Daldorf; but on minute examination it proves to be a species unknown in India, and hitherto found only in Boreno and China. It is the A. oligolepis of Bleek.
But the faculty of becoming torpid at such periods is not confined in Ceylon to the crocodile sand fishes;—it is also possessed by some of the fresh-water mollusca and aquatic coleoptera. One of the former, the Ampullaria glauca, is found in still water in all parts of the island, not alone in the tanks, but in rice-fields and the watercourses by which they are irrigated. When, during the dry season, the water is about to evaporate, it burrows and conceals itself[3551] till the returning rains restore it to activity, and reproduce its accustomed food. There, at a considerable depth in the soft mud, it deposits a bundle of eggs with a white calcareous shell, to the number of one hundred or more in each group. The Melania Paludina in the same way retires during the droughts into the muddy soil of the rice lands; and it can only be by such an instinct that this and other mollusca are preserved when the tanks evaporate, to re-appear in full growth and vigour immediately on the return of the rains.[3552]
Dr. John Hunter[3561] has advanced an 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 that imprisons the alligator in the Mississippi as effectually cuts it 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[3562] of Madagascar, its tropical representative, exhibits the same tendency during the period when excessive heat produces in that climate a like result.
The descent of the Ampullaria, and other fresh-water molluscs, into the mud of the tanks, 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.[3571] But exceptions serve to prove the accuracy of Hunter's opinion almost as strikingly as accordances, since the same genera of animals that 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.[3572] The shrews of Ceylon (Sorex montanus and S. ferrugineus of Kelaart), like those at home, subsist upon insects, but as they inhabit a region where the equable temperature admits of the pursuit of their prey at all seasons of the year, unlike those of Europe, they never hybernate. A similar observation applies to bats, which are dormant during a northern winter when insects are rare, but never become torpid in any part of the tropics. 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 in Venezuela immerses itself in indurated mud during the hot months shows no tendency to torpor in Ceylon, where its food is permanent; and yet it 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.[3581]
Hot-water Fishes.—Another incident is striking in connection with the fresh-water fishes of Ceylon. I have described elsewhere the hot springs of Kannea[3582], in the vicinity of Trincomalie, the water in which flows at a temperature varying at different seasons from 85° to 115°. In the stream formed by these wells M. Reynaud found and forwarded to Cuvier two fishes which he took from the water at a time when his thermometer indicated a temperature of 37° Reaumur, equal to 115° of Fahrenheit. The one was an Apogon, the other an Ambassis, and to each, from the heat of its habitat, he assigned the specific name of "thermalis."[3591]