24 



INBEEEDING- AND OUTBREEDING 



tandry). In the tapeworm (Fig. 3), for example, each 

 segment contains a complete reproductive system,, testes, 

 ovaries and accessory glands ; when young the testes func- 

 tion, when older the testes atrophy and the ovaries de- 

 velop. In some of these protandrous species there is 

 even a change in the whole structure of the body, includ- 



vaq 



Fig. 3. — Hermaphroditism in the tapeworm proglottid. K, genital pore; ou, ovary; ra, 

 receptaculum seminalis; (, testes: u, uterus; ud, Vas deferens. (Kingsley after Sommer). 



ing the sexual orifices. The isopods of the family Cymo- 

 tJioidce, a group of crustaceans parasitic on fish, furnish 

 a beautiful illustration. In the male stage the animal is a 

 typical crustacean and would be recognized as such by 

 any layman with a very slight laiowledge of zoology; but 

 when the animal passes over into the female stage it be- 

 comes merely a great egg sac many times the previous 

 size. One would hardly suppose the two stages belonged 



