STRUCTURE AND FUNCTION 71 



11. Contrast a cross section of hydra with one of earth- 

 worm as to the number of cavities. Which seems to you 

 the better plan ? Why .■' 



12. Why does a nereis need more respiratory surface 

 than an earthworm does ? 



13. Comparing earthworm and nereis, in what respects 

 is the earthworm degenerate .' How does it manage to 

 succeed so well with such a degenerate body .-' 



14. What is a parasite ? How many hosts does a 

 typical parasite require for its development .-" Which 

 host is known as the intermediate one .■' 



15. Trace the history of a tapeworm from the egg to 

 the adult. At what stage are they most likely to be 

 destroyed .' What provision is there for this .' What 

 advantages are there to the host in the fact that a tape- 

 worm's egg cannot develop in the original host.' What 

 advantages to the parasite .' 



16. What organs has a parasite lost, if it ever had 

 them ? How does it succeed without them .' What con- 

 nection is there between parasitism and degeneration.' 

 Can you decide which is cause and which is effect ? If so, 

 which is ? 



1 7. Why do worms so easily become parasitic ? What 

 advantages are there in becoming a parasite? What 

 disadvantages .■' 



18. What is radial symmetry.' Name two animals 

 which show it. What is bilateral symmetry .' Name two 

 animals which show it. What is the relation between 

 locomotion and symmetry ? 



19. What is meant in biology by the term "regenera- 

 -tion.'" To what extent have we this power? To what 



extent have hydra and earthworm ? What are the results 

 of this power ? 



