32 



ANIMAL FORMS 



striction soon occurs which 

 separates the young from the 

 parent, and from that time 

 on the two lead independent 

 existences. At other times 

 this asexual method of mul- 

 tiplication is replaced by sex- 

 ual reproduction, where new 

 individuals arise from fertil- 

 ized eggs. Both eggs and 

 sperm arise in Hydra and in 

 some other animals in the 

 same individual, but in all 

 such cases the eggs are fertil- 

 ized by sperm which escape 

 from some other individual. 

 The fertilized egg, surround- 

 ed by a firm coat, separates 

 from the parent, drops to the 

 bottom, and after a period of 

 rest develops into a little Hy- 

 dra which hatches and enters 

 upon a free existence. 



FIG. 17. Different types of Hydrozoan 

 colonies. From Nature, the lower 

 species magnified about 50 diameters. 



