I 



chj:tognatha 



869 



way the two primitive cells of the testes are also pushed 

 Lckwards (Fig. 161 C), whereas the primitive cells of the 



-Sd 



Fig. 161.— Tliree embryos of Sagitta at the sta','e of the formation of the germ- 

 layers, in frontal section (after O. Hkrtwig, from Lang's Lehrbuch). hi, blasto- 

 pore; ud, archenteron; g, primitive cells of the sexual organs ; vm, visceral 

 (.splanchnic), pr>i, parietal (somatic), laj-er of the mesoderm ; d, fundament of the 

 mid-gut; cs, coelomic sacs ; st, stomodajum (fore-gut). 



ovaries lie at the sides of the folds and in this way are 

 moved rather into the pair of coelomic sacs, in accordance 

 with their subsequent permanent position (Fig. 162). The 

 embryo bends more and more towards the ventral side, 

 during which a ventral ectodermal thickening becomes 



Fig. 162. -Dorsal and lateral views of an advanced embryo of Sagitta (after 

 BtJTSCHLi, from Ba-t^vovr's Comparative Embryologx)}. m. mouth j al, intestinal 

 canal; vg, fundament of the ventral ganglion; ey, ectoderm; c.pr, ct pi. alio 

 part of the body cavity ; so, somatic, ?p, splanchnic, layer of the mesoderm 

 ge, sexual organs. 



K. H. E. B B 



