168 CCELENTERATES. HYDRA-LIKE ANIMALS 
QUESTIONS 
Explain fully how the hydra gets its food and how some of this food 
finally nourishes the ectoderm cells. Compare the hydra and the 
hydroid. In what are they alike? In what are they different? How 
does the hydra reproduce? How does the hydra get its oxygen? Ex¬ 
plain how the coral animal has been able to form islands. 
REFERENCES 
Darwin, Structure and Distribution of Coral Reefs. 
Hegner, Introduction to Zoology, Chapter VIII. 
