248 



PLATYHELMINTHES. 



the last become, by their gradual shortening and the approach of 

 the longitudinal trunks, transformed into the vesicle, which acquires 

 an external opening when the segment behind it is detached. In 

 rare cases the excretory system possesses additional openings in the 

 anterior part of the body behind the suckers, and elsewhere. 



The generative apparatus is repeated in each proglottis. The 

 male apparatus consists of numerous small vesicles, the testes (Fig. 

 201, T), which are situated nearer one surface of the proglottis than 

 the other ; this surface is distinguished as the dorsal surface. 

 Delicate ducts proceed from the testes to open into a common efferent 



FIG. 201. Proglottis of Taenia saginata, with male and female organs (after Sommer). 

 Ov ovary ; Ds yolk-gland (vitellarium) ; Sd shell-gland ; Ut uterus ; T testes ; Vd vas 

 deferens ; Cb pouch of the cirrus ; K generative cloaca ; Va vagina. 



duct (vas deferens). The coiled end of this duct lies in a muscular 

 pouch (cirrus sheath), whence it can be protruded through the 

 genital opening as the so-called cirrus. This cirrus is frequently 

 beset with spines which are directed backwards, and serves as a 

 copulatory organ. The female generative organs consist of ovary, 

 yolk-gland, shell-gland, uterus, receptaculum, and vagina. The vagina 

 and vas deferens usually open into a common genital cloaca, which 

 lies either on the ventral surface of the segment (Bothriocephalus), 

 or on the lateral margin (Taenia) (Fig. 201). In the last case it may 

 be placed alternately on the right and on the left side. Sometimes 

 the two genital openings are widely separate, the male opening being 



