156 



COMPARATIVE ANATOMY 



CHAP. 



the germaria, of which' only 2 remain ; but as these have only to 

 yield eggs without yolk, they are quite sufficient in number. They 

 generally lie at the anterior end of the body, whilst the vitellaria 

 always occur in the lateral parts of the body between the intestinal 

 branches. 



In the Rhahdoccelidm the germ-preparing organs are considerably 



cv— 



Tig. 111.— Sexual organs of a Polyclad 

 (Leptoplana). To the left only the female, 

 to the right only the male organs are depicted. 

 0, Ovaries ; oy, oviduct ; i(, uterus ; ?i, 

 testes ; vd, vasa deferentia ; sb, seminal 

 vesicle; p, penis; id, shell gland; mo, male, 

 sexual aperture ; wo, female aperture. 



Fig. 112. — Sexual organs 

 of a fresh -water Planarlan 

 (Triclad). is, Germaria; ds, 

 vitellaria ; h, testes ; ov, ovi- 

 duct ; vd, vasa deferentia ; p, 

 penis ; go, common external 

 genital aperture. 



reduced in number, but on the other hand are, in relation to the body, 

 much larger than the single ovaries of the Polyclada. Many forms 

 possess ovaries only. The Accela, and the Macrostoniid(s among the 

 Rhaldocoda, have 2 lateral ovaries, the Microstomidm only 1 ovary. 

 In many Ehabdocfelida so-called germ-vitellaria attain development, 

 one often clearly separated portion of the ovary yielding only egg 

 germs, the other only yolk. 



One single germ-vitellarium is found in the Prorhynchidce. Proxenetes among the 

 Mesostomidce, Schultzia among the Vorticiclm, and Cylindrostoma among the Plagio- 

 stomidce possess two. 



