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 Rhahloccelidce the germ-preparing organs are considerably 



FIG. 111. Sexual organs of a Polyclad 

 (Leptoplana). To the left only the female, 

 to the right only the male organs are depicted, 

 o, Ovaries ; oo, oviduct ; u, uterus ; h, 

 testes ; /, vasa deferentia ; s6, seminal 

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

 sexual aperture ; wo, female aperture. 



FIG. 112. Sexual organs 

 of a fresh -water Planarian 

 (Triclad). l-s, Germaria ; ds, 

 vitellaria ; h, testes ; ov, ovi- 

 duct ; vd, vasa deferentia ; p, 

 penis ; #0, 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 Polydada. Many forms 

 possess ovaries only. The Accela, and the Macrostomidce among the 

 lihabdoccela, have 2 lateral ovaries, the Microstomidce only 1 ovary. 

 In many Ilhabdoccelidce 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 Prorhynchidcc. Proxenetes among the 

 Mesostomida:, ScJniltzia among the Vorticidce, and Cylindrostoma among the Plagio- 

 stomidce possess two. 



