Chap. X.] AESTIVATION OF MOLLUSCS. 
357 
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 over- 
arching 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 aestivation. 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 afresh 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 
exceptions serve to prove the accuracy of Hunter's opi- 
nion almost as strikingly as accordances, since the same 
genera of animals that hybernate in Europe, where ex- 
treme cold disarranges their oeconomy, evince no symp- 
toms 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), like 
1 Annals of Natural History, in the Entomological Trans, the 
1850. See Dr. jBaied's Account of operations of an ant in India which 
Helix desertorum; Excelsior, #c., lays up a store of hay against the 
eh. i. p. 345. rainy season. 
2 Colonel Sexes has described 
A A 3 
