[Footnote 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. [Footnote 1: HUNTER'S _Observations on parts of the Animal Oeconomy_, p. 88.] [Footnote 2: _Centetes ecaudatus_, Illiger.]