ANATOMY OP THE CESTODA 



293 



Genital Organs. With the exception of one genus (Dicecocestus, 

 Fuhrm.), in which the species are sexually differentiated, all the 

 Cestodes are hermaphroditic ; the genitalia 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 proglottids generally do not exhibit even traces of genitalia : 

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

 ment proceeds onwards from segment to segment. In a few ex- 

 ceptional cases (Ligula) the sexual organs are already developed in 



T. 



Vag. 



Vsc. 



Shg. 



FIG. 191. Proglottis of Tcenia saginata, Goeze, showing genitalia. C., trans- 

 verse excretory canal ; IV., lateral longitudinal nerve ; IV., longitudinal excretory 

 canal ; T., testicles scattered throughout the proglottis ; #., opposite the central 

 uterine stem (a closed sac) ; Ss. , genital pore leading into the genital sinus ; above 

 the cirrus and coiled vas deferens (V.d.), below the vagina (Vag.), bearing near 

 its termination a dilatation, the seminal receptacle; Vsc., the triangular vitel- 

 larium, and above it (Shg.) the shell gland ; leading from this to the uterus is seen 

 the short uterine canal, on either side of this the two lobes of the ovary (Ov.). lo/l. 



the larval stage, but are only functional after the entry of the parasite 

 into the final host. 



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

 uterus, all the parts of the genital apparatus lie in the medullary layer, 

 except only the vitellaria, which 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 lie dorsal to the median plane 

 (fig. 185, T.) ; a vas efferens arises from each testis, unites with 



1 There are, however, tapeworms with only one, others with only two or three testes 

 in each segment. 



