52 INVERTEBRATE ZOOLOGY 



ovaries are easily detected by the presence of large ova in 

 them. These are in groups of four, of which but one, the 

 third, is destined to become an egg, the other three being 

 nutritive cells by which it is nourished. In the male the testes 

 occupy a position similar to that of the ovaries. Their external 

 openings are on the ventral side of the abdomen. 



During the greater part of the summer the eggs pass into the 

 brood-pouch unfertilized and develop there parthenogenetically, 

 producing only females. The young animals pass out of the 

 brood-chamber through a posterior opening ; they soon become 

 adult and in their turn give birth to parthenogenetic females. 

 The eggs which thus develop are called summer eggs. At cer- 

 tain times of the year, however, as in the autumn, males are 

 also born. They fertilize the females, and the fertilized eggs 

 then produced differ from those which were unfertilized in 

 possessing thicker shells. They are called winter eggs and are 

 able to resist the cold of winter or the effect of drought. In 

 the springtime the winter eggs develop into parthenogenetio 

 females again. 



Exercise 3. Draw an outline of the animal and place in it all 

 the internal organs you have observed. 



