TORPIDITY. 77 



the period during which they may remain in this dormant 

 state. 



Since reptiles are easily acted upon by a cold atmos- 

 phere, we find but few of these animals distributed in the 

 cold countries of the globe ; while in those countries enjoy- 

 ing a high temperature they are found of vast size, and of 

 many different kinds, and in great numbers. 



The torpidity of the Mollusca has not been studied with 

 care. Those which are naked and reside on the land, re- 

 tire to holes in the earth, under the roots of trees, or among 

 moss, and there screen themselves from sudden changes of 

 temperature. The different kinds of land Testacea, such 

 as those belonging to the genera Helix, Bulimus, and Pupa, 

 not only retire to crevices of rocks and other liiding places, 

 but they form an operculum or hd for the mouth of the 

 shell, by which they adhere to the rock, and at the same 

 time close up even all access to the air. If they be brought 

 into a warm temperature, and a little moisture be added, 

 they speedily revive. In the case of the Helix nemoraliSy 

 the operculum falls off when the animal revives, and a new 

 one is formed, when it returns again to its slumbers. The 

 first formed opercula contain a considerable portion of car- 

 bonat of lime, which is found in smaller quantity in those 

 generated at a later period. If the animal has revived fre- 

 quently during the winter, the last formed opercula consist 

 entirely of animal matter, and are very thin. The winter lid 

 of the Helix pomatia resembles a piece of card-paper. 



All the land testacea appear to have the power of be- 

 coming torpid at pleasure, and independent of any altei*a- 

 tions of temperature. Thus, even in midsummer, if we 

 place m a box, specimens of the Helix hortensis, 7iemoralis 

 or cu'bustonim, without food, in a day or two they form 

 for themselves a thin operculum, attach themselves to the 

 side of the box, and remain in this dormant state. They 



