23 



ELEMENTARY ZOOLOGY. 



249. Topics for Themes in Zoology and English. i. 



Can you show any relation among mollusks between the 

 presence of external protective structures and the degree 

 of activity? 



2. What grounds are there for believing that the 

 lamellibranchs are degenerate mollusks? 



FIG. 78. The Devil-fish (Octopus). From Cooke. A, at rest;. B, swimming, a, 

 arms, with suckers on the inner side; e, eye; s, siphon or funnel. 



Questions on the Figure. Which is the anterior end of the animal ? 

 What is the position of the mouth? What is the function of the 

 siphon? Of what structure is it a part? Compare the devil-fish 

 with the squid, through figures. 



3. In what ways may the land snails have arisen from 

 the original marine forms? 



4. Write a more extended account of the economic 

 value of mollusks. 



5. Write an account of "oyster farming" and the con- 

 ditions that are favorable for it. How does the oyster 

 of our Atlantic coast compare with other oysters? 



