CESTODES I GENERATIVE ORGANS 



197 



Generative Organs. With the exception of one genus (Diceco- 

 cestus, Fuhrm.), which is stated to be sexually differentiated, all 

 the cestodes are hermaphroditic ; the genitals first develop gradually 

 in the segments (never in the scolex), the male organs, as is usual 

 in hermaphroditic animals, forming earlier than the female. The 

 youngest proglottides generally do not exhibit even traces of 

 genitals; these, as a rule, develop first in the older segments, and 

 the development proceeds onwards from segment to segment. In a 

 few exceptional cases (Ligtda] the sexual organs are already 



N. 



Ut, 



Vag, 



Vsc. Shg. 



FIG. 1,25. Proglottis of Tcenia saginata, G., with genital organs. 10/1. 

 C-, transverse canals of the excretory system ; Ss., genital pore ; Vsc., vitellogene 

 gland; T., testicles; N., lateral longitudinal nerve; Ov., ovary; Shg., shell gland ; 

 Ut., uterus ; Vag., vagina ; V.d., vas deferens ; W., excretory vessel. 



developed in the cysticercus stage, but are only functional after the 

 introduction of the parasite into the terminal host. 



With the exception of the end portions of the vagina, cirrus 

 and uterus, all the parts of the genital apparatus lie in the medul- 

 lary layer ; only the vitellaria in many species are in the cortical 

 layer. The male apparatus consists of the testes, of which, as a 

 rule, there are a large number, 1 and which are in a dorsal position 

 from the transverse plane (fig. 119, T.), a vas efferens springs 



1 There are, however, tape-worms with only one, others with only two or 

 three testes in each segment. 



