MOLLUSCA. 23 



been observed to thrive on the food which it spontaneously 

 yields, to execute their accustomed motions, and above all, 

 to propagate their kind, we shall be disposed to conclude, 

 that patient suffering has been mistaken for health and 

 vivaciousness for the power of accommodation. 



The influence of the seasons, in regulating the motions 

 and habits of molluscous animals, has been but little attend- 

 ed to. Those which live in the water, avoid the effects of 

 low temperature, on the approach of winter, by retiring to 

 the deeper parts of the lakes or rivers in which they reside. 

 This migration, however, does not, in many cases, furnish 

 the requisite security, so that they betake themselves to 

 burrowing in the mud in which they repose until increasing 

 warmth invites them to return to the open water. 



Among the naked terrestrial mollusca, it may be observ- 

 ed, that they burrow in holes of the earth, under the roots 

 of trees or among moss, and there screen themselves from 

 sudden changes of temperature, and appear to spend the 

 winter in a state of torpidity. 



The different kinds of shelly mollusca which inhabit the 

 land, such as those belonging to the genera Helix, Buli- 

 mus, and Pupa, not only retire to crevices of rocks and other 

 places, for safety in the winter season, but they form an 

 operculum or lid for the mouth of the shell, calculated to 

 exclude the access of the air, and by the intervention of 

 which they likewise adhere to the wall of their dwelling. A 

 rise of temperature, however, especially if accompanied by 

 moisture, excites their revival and motion, and the lid be- 

 comes detached. If we bring, for example, the Helix ne- 

 moralis, from its cold abode, and in an apparently torpid 

 state, with the mouth of its shell closed by the lid and ad- 

 hering to a stone, into a warm apartment, it will speedily 



