8 CALIFORNIA 8EA SHELLS. 



The Gasteropods are usually provided with 

 elementary eyes, placed upon two tentacles or 

 feelers ; when disturbed they can quickly with- 

 draw these eyes, and if much alarmed, all the 

 soft parts retreat within the shell, and the aper- 

 ture is closed by a little door called the operclum. 

 If undisturbed lor a little while, they venture out 

 again, and crawl by means of a broad muscular 

 disk or foot, the parts ot which advance in little 

 waves. Some mollusks construct curious egg 

 cases, others throw their ova into the water, or 

 hatch them in their own gills. The young gen- 

 erally have the power of locomotion, at least for 

 a few hours, after which, the stationary kinds 

 settle down tor life, in their proper abodes. By 

 means of this free early life, many species are 

 rapidly spread over large areas. We must not 

 omit to mention the land Gasteropods, such as 

 snails and sings. These breathe air by means of 

 a simple lung, feed on vegetables, and lay their 

 eggs under dead leaves and in similar positions. 



The early naturalists classified mollusks 

 almcst wholly by their shells, but investigation 

 has shown that some species whose shells are 

 quite similar are very different in regard to their 

 more vital organs, and by modern writers they 

 have been arranged more nearly in their true 

 position. Still, in most mollusks the shell gives 

 pretty correct information in regard to the nature 

 of the animal of which it forms a part. Besides, 

 the shell is the most conspicuous and enduring 

 part of the mollusk, and preserves its form and 

 color indefinitely ; while the soft parts must be 

 preserved in alcohol, and then they shrivel and 

 change their color. 



