GENITAL ORGANS. 



315 



The crenital cells shift later into the interior of the coelomic sacs, 

 soon reaching their dorsal Avail (Fig. 169 A, gz) and passing in 

 between its cells. The coelomic sacs (c), in transverse section, at 

 this stage are approximately triangular in outline, so that we may 

 distinguish a dorsal (dw), a lateral (Iw), and a median wall (mw). 

 The dorsal wall is in contact with the surface of the yolk, and 

 later, by delamination, yields the splanchnic mesoderm (Fig. 170, sp), 

 while from its remainder is formed the terminal filament of the 



Fig. 171.— Transverse section through the abdomen in an older germ-band of Phyllodromia 

 gernianiea, in the stage when the circumcrescenee of the yolk commences (after Hetmons). 

 bg, ventral chain of ganglia ; c, remains of the coelomic cavity ; ez, rudiment of the efferent 

 genital duct; ef, terminal filament; en, entoderm; fk, fat-body; gz, genital cells; h, rudi- 

 ment of the heart ; ps, pericardial septum ; sp, splanchnic mesoderm ; vm, ventral 

 longitudinal muscle. 



genital gland (ef). The lateral wall, which is parallel to the germ- 

 band, takes an active part in the formation of the somatic layer 

 (Fig. 169 C, so) of the mesoderm, the pericardial septum being 

 eventually derived from what remains of it (Fig. 170, ps). 



When the genital cells have entered the dorsal wall of the 

 primitive segments, they are already so numerous as to form a 

 continuous strand running from before backward. The genital 



