200 



THE ANIMAL PARASITES OF MAN 



but with the accumulation of eggs it becomes modified in various 

 ways ; it sends out lateral branches, sometimes also forms numerous 

 little diverticula which shelter single eggs or groups of eggs. This 

 part of the female genital apparatus is not immediately confined 

 to the spot where the eggs are formed, but a narrow passage, the 

 uterine canal, intervenes between the two. 



In species in which the uterus lacks an opening, simultaneously 

 with the growth of this organ an atrophy of the male apparatus, 

 at least of the testes and their excretory ducts, takes place ; this 

 atrophy also frequently occurs in the female germinal glands, so 

 that the entire mature segments have only separate residues of 

 the genitals left, with the exception of the uterus. 



In the Acoleinae the vagina is more or less further atrophied, 

 and in any case has no external opening. 



A number of genera are distinguished by the duplication of 



Vvs. 



FIG. 128. Part of a transverse section through a proglottis of Dibothrio- 

 cephalus latus. . 20/1. Ct. t cuticle; C., cirrus; Vvs., vesicles of vitellogene gland ; 

 Lm., longitudinal muscles ; T., testicles ; M., medullary fasciculus ; Sc., sub- 

 cuticle ; Tm., transverse muscles : Ut. t uterus. 



the genitalia in every segment ; the genital apparatus in its entirety, 

 or with the exception of the uterus, is double, or the genital glands 

 and the uterus are single, but the cirrus, vas deferens and vagina 

 are duplicated. 



On comparing the genitalia of the trematodes and cestodes the 

 parts will be found to agree, but the vagina of the cestodes 

 corresponds to the uterus of the trematodes, and the uterus of the 

 tapeworms to Laurer's canal of the trematodes ; which in most 

 of the cestodes has lost its external orifice. 



DEVELOPMENT OF THE TAPEWORMS. 



Copulation. As each proglottis possesses its own genital apparatus 

 and male as well as female organs are united, the . following pro- 



