8 
CALIFORNIA SEA 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 for 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 slugs. 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 
almost wholly by their shells, but investigation 
has shown that some species w T hose 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. 
