Ill 



PLATODES SEXUAL ORGANS 157 



In the greater number of Rhabdoccda and Allcdoccela, however, 

 there is a complete separation into germaria and vitellaria. The 

 germaria are mostly small and round, the vitellaria (ds) are large, often 

 lobate, branched or reticulate. The vitellaria are generally double ; 

 where they are single reticulate branched masses, their originally double 

 condition can be recognised by the duplication of their efferent ducts. 

 The germarium is either double or single. 



One germarium is found in most Mesostomidce, Gyrator among the Proboscidea, 

 most Vorticidce,and Solcnopharynx. Two are found in Promesostoma, most Probos- 

 cidea, Provortex and Graffilla among the Vorticidce, and the Alloiocosla. 



Separate germaria and vitellaria are found in all Trematoda and 

 Cestoda. The germaria (Figs. 114 and 115, ks) are either simply 

 round, or lobed, or branched. The vitellaria (ds) are mostly (excepting 

 in the Teenies) very extensive, and branched in a reticulate manner, or 

 else broken up into a large number of small globular bodies or saccules. 



The Trematoda possess a median germarium and 2 lateral vitellaria, 

 the Cestoda 2 germaria and either 2 lateral vitellaria or a small posterior 

 vitellarium (Tcenice). 



II. The male germ elements or testes are present in the Polyclada 

 (Fig. Ill, h) in greater numbers than the ovaries. They always lie 

 in the lateral parts of the body between and under the intestinal 

 branches. The same holds good of the numerous testes of the Triclada 

 (Fig. 112, h). In Gunda segmentata the testes lie on each side in a 

 single longitudinal row in the dissepiments which separate the con- 

 secutive intestinal branches. They thus repeat themselves in the 

 body just as regularly as do the intestinal branches, dissepiments, 

 transverse commissures of the nervous system, and the external aper- 

 tures of the water-vascular system. In the Rhabdoccelidce there are 

 either 2 testes (Fig. 113, h, Rhabdocoda), or the testes are broken up 

 into numerous lobes or vesicles, which are scattered in the parenchyma 

 (Acoela, Alloiocoela). Nearly all Trematoda (Fig. 114, h) possess 2 

 round, or lobed, or branched testes, while in the Cestoda (Fig. 115, h) 

 there are numerous scattered testicle vesicles. 



B. The Efferent Duets of the Sexual Products. 



The Female Duets. The female sexual glands are produced into 

 tubular ducts, which collect the sexual products and carry them to the 

 exterior. The ducts are either egg ducts (oviducts) when they pro- 

 ceed from the ovaries or germaria, or yolk ducts (vitello-ducts) when 

 they carry out material formed in the vitellaria. The anatomy of this 

 part is so varied that we can only select the most important points. 



In the Polyclada (Fig. Ill) numerous oviducts (ov) proceed from 

 the numerous ovaries. These ducts frequently unite to form larger 

 ducts, which again enter more spacious tubes, generally running in the 

 longitudinal direction on both sides of the middle line. Numerous 



