44 



MOLLUSC A. 



ming animals, living for the most part off shore, and 

 most species come to the surface only at night. 



Common snails can be easily procured in damp, 

 shaded places, and in the woods ; but the best speci- 

 mens are the edible snails, imported to New York from 

 France, and our common garden snail. They should 

 be drowned by immersion in fresh water under a close 

 cover. 



In this situation they die slowly, and apparently 

 with as little pain as possible. The parts are distended 

 with water, and in good condition for examination. 

 The pupil will naturally observe with curiosity the coiled 

 shell, and the large crawling disc or foot. 



These observations, in fact, ought to be made upon 

 a live snail, and repeated upon the dead ones, which 

 will then be better understood, and studied with a 

 more lively interest. 



The shell, in the first place, will be seen to be 

 brownish, or of various colors, on the outside, and the 

 fact that this coloring resides in an external horny 

 layer, like that of the oyster and clam, established by 

 scratching it a little with a knife. 



The opening of the shell will be found to be entire, 

 like the flaring mouth of a trumpet ; and thus, if there 

 is an empty shell, also, which can be examined, atten- 

 tion can be called to the difference between this single 

 shell, which is like a cone coiled into a spiral, and the 

 two valves of the Lamellibranchiata. The names 

 "univalve" and "bivalve" are often applied to the 

 snails and oyster in popular literature without any ade- 

 quate appreciation of their real meaning. The snail 

 shell (Fig. 48) does not correspond to one valve of the 



