GENITAL ORGANS. 



343 



—•jo 



Fig. ICO. — Transverse section through the abdomen in three consecutive stages of develop- 

 ment of Phyllodromia germanica (after Heymons). am, amnion ; bg, rudiment of the 

 ventral chain of ganglia ; c, coelomic cavity ; c', dorsal, and c", ventral sections of the 

 coelomic sac ; cz, cells of the wall of the primitive segments, applied to the ventral side 

 of the genital rudiment ; d, food-yolk ; dw, dorsal wall of the coelomic sac ; ec, ectoderm ; 

 ep, epithelial cells ; ex, abdominal limb-rudiments ; /, rudiment of the fat-body ; gz, genital 

 cells ; Iw, lateral wall of the coelomic sac ; m, mesoderm-cells, which do not take part in 

 the formation of the coelomic sacs; miv, median wall of the coelomic sac; so, somatic 

 mesoderm-layer ; vm, ventral longitudinal muscle. 



