298 



EMBRYOLOGY 



liberated one by one (Fig. 138 B), and either undergo their 

 further development while floating free in the body cavity, 

 or, as in the case of the testicular cells of the earthworms, 

 reach special vesicles (vesiculge seminales), which, according 

 to Bergh (No. 5), arise on the septa by means of a process 

 of growth and invagination. 



The ducts of the sexual organs are to be looked upon as 

 more or less modified segmental organs. They arise in the 



^« 



/m.. 



B. 



g.(lr 



pm.. 



Yv. 



i4MM^i 



g.ar. 



Fio. 138.—^ to D, diagrammatic representation of the structure and development 

 of an ovary of An\y)iiiyite \uhra (after E. Mbybb). g.dr, sexual gland ; g.«, genital 

 epithelium; g.z, genital cells in the act of breaking away; pm, peritoneum; Y.v, 

 vas ventrale. 



same way as the nephridia themselves, except that the 

 funnel is formed earlier than in the actual segmental organs 

 (Vljdovsky). The entirely independent origin of the efferent 

 sexual ducts from the nephridia and the simultaneous occui*- 

 rence of both organs in the same segment, as happens in the 

 earthworms, form no argument against the origin of the 

 ducts from nephridia, since in some Annelida (Capitdlidde, 

 according to Eisiu) several pairs of nephridia occur in the 

 same segment. In the earthworms especially, many things 



