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 

 dn 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 ceconomy, 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. Baied's Account of operations of an ant in India which 



Helix desertorum ; Excelsior, #c, lays up a store of hay against the 



<ch. i. p. 345. rainy season. 



8 Colonel Skyes has described 



A A 3 



