330 



PLATTIIELMINTHES. 



FIG. 266. Ripe proglottides ready to separate. 

 n, of Tffnia folium ; b, of Tcenia mediocanellata ; 

 We, watervasciilar (excretory) canal. 



genital cloaca, which lies either on the ventral surface of the segment 

 (Bothriocepalits), or on the lateral margin (T(enia) (tig. 265). In 



the last case it is placed alter- 



b 



nately on the right and on the 

 left side. Nevertheless it may 

 happen that the two genital 

 openings are widely separate, 

 the male opening being placed 

 at the side, the female on the 

 surface of the segment. As 

 the segments increase in size 

 and become further removed 

 from the head, the contained 

 generative organs gradually 

 reach maturity in such a way 

 that the male generative 

 organs arrive at maturity 

 rather earlier than the female. 

 As soon as the male elements are mature, copulation takes place, and 

 the receptaculum seminis is filled with sperm, and then only do the 

 female generative organs reach 

 maturity. The ova are fertilized 

 and pass into the uterus, which 

 then assumes its characteristic 

 form and size. As the uterus 

 becomes distended, the testes and 

 then the ovaries and vitellaria are 

 more or less completely absorbed 

 (fig. 266). The posterior proglot- 

 tides, viz., those which are ready 

 for separation, have alone under- 

 gone full development, and the 

 eggs in their uterus often contain 

 completely developed embryos. 

 Accordingly we can recognize in 

 a continuous series of the seg- 

 ments the course of development 

 passed through by the sexual 

 organs and products in their 

 origin and gradual progress towards maturity. The number of 

 segments between that with the first trace of the generative organs 



FiG.F[267. Egg with embryo (a) of Tcenia 

 toliuni; (b) of Microtcen itt ; (c), of Sothrio- 

 eephalim lufiis (after R. Leuckart). 



