, which
formed pools on the surface of the ground near a mango grove, he saw the
_Paludinae_ 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 _Ampullariae_ and
_Planorbes_, as well as the _Paludinae_, 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.]

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