SQUIDS, CUTTLE FISH, AND OCTOPI 
191 
Figure 178. — Soft-shelled Clam. 
Much prized as food. I.S., incurrent siphon ; E.S., excurrent siphon. 
Note the clam’s foot. 
then eaten. Snails also gnaw away the surface of the water 
plants with their rasp-like tongue (Figure 176). 
These snails lay eggs in jelly-like masses that stick to the 
leaves of plants. The 
jelly-mass protects the 
developing embryos and 
furnishes food to the 
young snails. As soon 
as the young of Physa 
are fully formed they 
escape from the jelly- 
mass and are able to care 
for themselves. 
181. Squids, Cuttle 
Fish, and Octopi belong 
to the Cephalopods (sef'a- 
lo-pods: Greek, kephale, 
head; pod , foot), the 
highest division of the mollusks. The nervous system is 
highly developed. The eye of the squid in particular is 
complex and more like the eye of vertebrates than of any 
Figure 179. — An Octopus or Devil¬ 
fish. 
