6o A GUIDE FOR THE STUDY OF ANIMALS 



3. What enables a hydra to stick to a support by its 

 foot ? 



4. What are the processes in a hydra by which food 

 is captured, swallowed, and digested ? 



5. What is the chief fact of interest about Hydra 

 viridis ? 



6. Why do hydras reproduce all summer by budding 

 and in the late fall by eggs ? 



7. What change would have developed a hydra and its 

 offspring into a plant-like colony instead of into a group of 

 individuals ? 



8. Why are ctenophores more easily seen in the night 

 than other ccelenterates are ? 



9. What relations may exist between hydroids and 

 hydro-medusae ? 



10. What are the advantages of a sedentary life ? Of 

 a locomotory one ? 



11. What is meant by the expression "alternation of 

 generations " ? Which animals are likely to develop alter- 

 nation of generations, sedentary ones or locomotory ones ? 

 Why? 



12. Give at least two differences between hydro-medusae 

 and true jellyfishes. 



13. In the association between a hydractinia colony and 

 a hermit crab, what advantages are derived by the hy- 

 dractinia ? by the crab ? Define symbiosis. Give another 

 illustration of it. 



14. How are new coral colonies started ? How are 

 large colonies formed .■' 



15. What are the conditions of life under which corals 

 can grow vigorously .■' 



16. Where are corals most abundant .' 



/\r(?U. — Show by coloring the regions on a blank map of the world. 



MM 



