PHYLUM PLATYHELMINTHES 



141 



wards from its point of origin, it gradually develops the 

 various parts of the reproductive apparatus in its interior, 

 until, when it has reached the posterior region, it possesses a 

 complete set of reproductive organs, and, as it reaches the 

 extreme posterior end, it has become ripe, /.<?., has its uterus 

 distended with eggs. 



In the interior of each of the eggs in the ripe proglottides 

 is an embyro consisting of a rounded mass of cells bearing 

 six chitinoid hooks the six-hooked or hexacanth embryo 



can-.excret 



ca.n.ejccret 



ne.ru.1 



FIG. 70. A proglottis of Taenia SOlium. with mature reproductive apparatus. 

 can. excret. longitudinal excretory canals with transyerse connecting vessels ; 

 gl. vit. vitelline glands ; nerv. 1. longitudinal nerves ; ov, ov. ovaries ; par. gen. 

 genital pore ; schld. shell-glands ; uter. uterus ; vag. vagina ; vas. def. vas 

 deferens. The numerous small round bodies are the lobes of the testes. (After 

 Leuckart.) 



(Fig. 71, A). After the egg has been discharged from the 

 free proglottis, it has to reach the enteric canal of a second 

 kind of animal a second or intermediate host in order that 

 the embryo may be enabled to enter the next phase of its life- 

 history. In the case of some Tape-worms, this second or 

 intermediate host is, like the first or permanent host, a 

 Vertebrate animal : in the case of others it is some Inverte- 

 brate animal such as an Earthworm, a Centipede, or an 



