FURTHER DEVELOPMENT OF THE MESODERM. 



319 



Fig. 15". — Transverse sections through the abdominal region of three consecutive stages in 

 development of Phyllodromia germanica (after Heymons). am, amnion ; [&</, rudiment of 

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

 coelomic cavity ; cz, cells of the primitive segments which become applied to the genital 

 rudiment ; <?, food-yolk ; dw, dorsal wall of the coelomic sac ; ec, ectoderm ; ep, epithelial 

 cells; ex, abdominal limb-rudiments; /, rudiment of the fat-body ;" gs.Tgenital cells; 

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

 formation of the coelomic sacs ; raw, median wall of the coelomic sac ; so, somatic mesoderm- 

 layer ; vm, ventral longitudinal muscle. 



