SQUIDS, CUTTLE FISH, AND OCTOPl 



99 



through rocks. Land snails by osmosis get oxygen from 

 the air through the mantle, while water snails use gills 

 and take their oxygen from the water. 



Figure 99. — Snail Shells. 



In the garden slug the shell when present is thin and 

 affords small protection. 



101. Squids, Cuttle Fish, and Octopi belong to the Cephalo- 

 pods (sefa-lo-pods : Greek, kephale, head ; pod, foot), the 

 highest division of the 

 mollusks. The nervous 

 system is highly devel- 

 oped. The eye of the 

 squid in particular is 

 complex and more like 

 the eye of vertebrates 

 than of any animal thus 

 far considered. The 

 mouth of cephalopods is 

 surrounded with ten- 

 tacles. 



A common squid, Figure 100. — An Octopus. 



