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- 











00 



ww, 



b3 



OOoSo O o CP O- 



&&$?%&%$<>&& 



4fo8?o^o<fl?^ 

 o.oo.o o_^ 



O OOOQC 



O o o o .. 

 oooo o 



OQ00 < 



O On ^ 



^-^ A ~n ^^ ~ v xC' O no 



^Vj^ooOol 

 'o " ooO 



^j!?? 



it. 



^wm^^^^ 



^fe ~fe:^ V f^ 



o;V59a 



y$&w$r&ss&$ 



FIG. 3. Hermaphroditism in the tapeworm proglottid. K, genital pore; ov, ovary; rs, 

 receptaculum seniinalis; t, testes; u, uterus; vd, vas deferens. (Kingsley after Sonimer). 



ing the sexual orifices. The isopocls of the family Cyyno- 

 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. 



