24 



INBREEDING 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- 



Fio. 3. Hermaphrpditism in the tapeworm proglottid. K, genital pore; or, ovary; r, 

 receptaculum seminalis; t, testes; u, uterus; td, vas deferens. (Kingsley after Summer). 



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

 thoidce, 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 knowledge 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 



