232 MOLLUSCA. 



in a perfectly horizontal position ; the foot is con- 

 tracted within the shell; the thick edge or collar 

 of the mantle is expanded over it, and is very white 

 and plump. In about an hour after the finishing 

 of the roof, the breathing-hole in the right side is 

 opened, and a quantity of air is inspired ; then, 

 closing the orifice, it forms a very thin and trans- 

 parent layer of slime, like a skin, between the sur- 

 face of the mantle and the substances outside. Pre- 

 sently, from the whole surface of the collar, is poured 

 out a copious fluid like thick cream, of a pure white, 

 which, covering the whole of the exposed part of 

 the animal, hardens immediately, and in the course 

 of an hour is become a perfectly solid operculum, 

 a little thicker than a wafer. The Snail now expels 

 a portion of the air it had taken in, and thus con- 

 tracting, retires farther into the shell, leaving a 

 chamber of air between it and the operculum. Here 

 it forms another layer of slime, which hardening into 

 a skin stretched across the shell, it expels more air 

 and retires farther, thus leaving another chamber, 

 and so on until sometimes even six of these partitions 

 are formed, inclosing cells filled with air. Two or 

 three days are occupied by a single Snail in these 

 operations ; but the whole of October is spent be- 

 fore all have finished, and by the beginning of No- 

 vember none are found abroad except such as from 

 disease have not sufficient strength to form their 

 retreat, and which perish with the first severe frost. 



In this snug habitation the Snail sleeps away six 

 months of the year, all unconscious of the wintry 



