PHYLUM PLATYHELMINTHES 



141 



terior end, and reach the exterior with the faeces of the 

 host. At the same time new proglottides are constantly 

 being formed by the appearance of new ring-like grooves 

 behind the neck region. This dropping off of ripe proglot- 

 tides from the posterior end, and the formation of new ones 

 behind the neck, results in a gradual shifting backwards of 

 the proglottides. As each proglottis passes backwards from 

 its point of origin, it gradually develops the various parts 

 of the reproductive apparatus in its interior, until, when 



can^.excret 



ca.n.excret 



■vas.def 



nerv.f 



ot, gl-vit sikioi ou 



Fig. 76. — A proglottis of Taenia solium with mature reproductive apparatus. 

 can. excret, longitudinal excretory canals with transverse connecting vessels; 

 gl. vit, vitelline glands; nerv. I, longitudinal nerves; ov t ov t ovaries; por. 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.) 



it has reached the posterior region, it possesses a com- 

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

 extreme posterior end, it has become ripe, i.e., has its uterus 

 distended with eggs. 



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

 is an embryo consisting of a rounded mass of cells bearing 

 six chitinoid hooks — the six-hooked or hexacanth embryo 

 (Fig. 77, A). After the egg has been discharged from the 

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



