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 sez- 
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. 
Fic. 17.—Different types of Hydrozoan 
colonies. From Nature, the lower 
species magnified about 50 diameters. 
