PHYLUM PLATYHELMINTHES 



267 



at 



lobes. There are no vitellaria in most cases the two ovaries 

 producing large ova containing abundant food-yolk and the sub- 

 stance of the egg-shell being formed from droplets in the latter. 

 Oviducts are absent in most cases. Into the main female genital 

 passage or antrum femininum opens a peculiar single or double sac 

 or bursa, usually provided with chitinous structures. In one case 

 at least (Heterochcerus) there is a 

 passage leading from the antrum 

 femininum to an aperture on the 

 dorsal surface. 



Most of the Trematodes have 

 two testes (reduced to one in Aspi- 

 docotylea and Heterocotylea), usually 

 compact, sometimes branched ; in 

 a few instances there are four. 

 The vasa deferentia unite into a 

 median duct, which is dilated at 

 the base of the cirrus to form a 

 vesicula seminalis^ There is a 

 single oval or branched ger- 

 marium, and two sets of vitel- 

 line glands. A canal termed 

 Laurer's canal in some Malaco- 

 cotyleans, such as some species 

 of Distomum, leads from the ex- 

 terior to the oviduct or vitelline 

 duct. This may be replaced by a 

 receptaculum seminis, or both 

 structures may co-exist. The 



Jistal part of the oviduct is en- 

 irged to act as a uterus. In the 

 leterocotylea there is a vagina, 

 which is sometimes paired, opening 

 on the surface independently of the 

 uterus : internally it communicates withjthe oviduct through the 

 main vitelline duct. In some of the Heterocotylea there is a genito- 

 intestinal canal occupying a corresponding position to Laurer's 

 canal, but opening into the intestine. In the Aspidocotylea this is 

 replaced by a stalked yolk-receptacle. There is nearly always a 

 genital atrium commop to the ducts of both sexes. 



In the Temnocephalea (Figs. 204, 205) there^aie a genital atrium 

 and a single genital aperture. There are two pairs of compact 

 testes ; the right and left vasa deferentia unite in a vesicula semi- 

 nalis, and granule or prostate glands are well developed. The 

 cirrus has a chitinous tube and a variety of ^veraiJ)le spines. There 

 is a single compact germarium ; the oviduct has connected with it 

 a large receptaculum, and dilates posteriorly to form an ootype into 



Tit 



FIG. 218. Reproductive organs of MCSD- 

 stomum ehrenbergii. dg. duct of 

 vitelline glands ; do. vitelline glands ; go. 

 common reproductive aperture ; ov. 

 ovary ; p. cirrus ; rs. receptaculum se- 

 minis ; s. pharynx ; t., t. testes ; ut. uterus; 

 vd. vas deferens. (From Claus, after von 

 Graff and Schneider.) 



