272 



ZOOLOGY 



SECT. 



Ut 



two compact testes and two vasa deferentia leading to the unpaired 

 male aperture at the extremity of the cirrus. The prostrate or 

 granule glands & set of unicellular glands, which secrete round, 



bright granules destined to mix 

 with the sperms are specially 

 well developed in the Rhabdo- 

 cceles, and are present in some 

 other Turbellaria and in certain 

 Trematodes. Ovaries (germ- 

 vitellaria) alone occur in some, 

 separate germaria and vitellaria 

 in others; there are either 

 two germaria or one only. A 

 receptaculum seminis may be 

 present as a swelling or diver- 

 ticulum of the main female duct, 

 or of the atrium. The terminal 

 part of this duct may form a 

 muscular vagina, or there may be 

 a muscular bursa copulatrix de- 

 veloped from the wall of the 

 atrium. A uterus is present in 

 most cases as an outgrowth from 

 the wall of the atrium. Male 

 and female ducts have a common 

 chamber or genital atrium with a 

 single external opening. 



In the Acoela there are in 

 nearly all cases separate male 

 and female apertures. The two 

 testes are divided into numerous small lobes. There are no 

 vitellaria in most cases the two ovaries producing large ova 

 containing abundant food-yolk. Oviducts are absent in most 

 cases. Into the main female genital passage opens a peculiar 

 single or double sac or bursa, usually provided with chitinous 

 structures. 



The Trematodes nearly all have two testes, 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 gernuzrium, and two sets of vitelline glands. A canal 

 termed Laurers canal in some Malacocoty leans, such as some 

 species of Distomum, leads from the exterior to the oviduct or 

 vitelline duct. This may be replaced by a receptaculum 

 seminis, or both structures may co-exist. The distal part of 

 the oviduct is enlarged to act as a uterus. In the Hetero- 

 cotylea there is a vagina, which is -sometimes paired, opening 



FIG. 215. Reproductive organs of Meso- 

 stomum Ehrenbergii. dg. duct of 

 vitelline glands ; do. vitelline glands ; go. 

 common reproductive aperture ; ov. ovary; 

 p. cirrus ; rs receptaculum seminis ; s. 

 pharynx ; t., t. testes ; ut. uterus ; vd. 

 vas deferens. (From Glaus, after von 

 Graff and Schneider.) 



