722 THE GENERATIVE ORGANS. 
As has already been pointed out, there are apparently closer 
affinities between the Insecta and the solid-bodied Worms, 
than between the Insecta and the Annelida, which are more 
frequently compared with them. 
The Turbellaria have the same spongy reticulum between 
their internal organs; as has been already stated, both the 
Wy : ami \\\ 
Sa AVIAN 
Ry 
Fic. 103.—Diagram of the generative organs of a Rhabdoccelian (after Graff). 
dc, bursa copulatrix ; g, germogen ; 7 S, receptaculum seminis 2; ¢, 4 testicles ; 
u, uterus ; 7, 2, vitellogen ; v s, vesiculus seminalis ¢ ; p> common genital duct. 
remarkable metamorphoses of Insects and some peculiarities 
of their embryo are foreshadowed in the Nemertid Worms ; 
and, lastly, the water vascular system of the solid-bodied 
Worms is probably the homologue of the tracheal system of 
the Insect (p. 358). 
Two phenomena are observed in the reproductive process in 
many Trematodes and in some Insects; these are asexual or 
* Planarians, Zool. article ‘Encyclopaedia Britannica,’ Lond., 1891. 
