264 



INVERTEBRATA 



CHAP. 



the surface. We find also an embryonic area from which nuclei are 

 budded off into the interior, but this area is very short indeed 



,9 



coe 



v.m 



FIG. 208. Transverse sections through three embryos of Fhyllodromia germanica at three 

 stages of development in order to show the development of the coelornic sacs. The 

 fat body, and the generative organs. (After Heymons.) 



A, the youngest stage. B, intermediate stage. C, oldest stage, after the completion of the dorsal 

 surface, coe, coelomic sac ; ep, epineural sinus ; f.b, fat body ; fil.p, terminal filament plate of the genital 

 organ ; g, germ cells ; gen, accumulation of germ cells forming the genital organ ; H, heart ; stig, stigma 

 of trachea ; v.m, ventral longitudinal nerve ; v.n.t, ventral nerve cord. 



compared to the length of the egg. The cells which are budded 

 inwards give rise to the yolk cells, and also to those cells which, at a 



fil 



FIG. 209. The rudiment of the female genital organs of Phyllodromia germanica 

 reconstructed from sagittal sections. (After Heymons.) 



Jil, terminal filament ; fil.p, plate uniting upper ends of the terminal filaments ; germ, germ cells ; 

 ovd, rudiment of oviduct. 



comparatively late period in development, assemble on the surface 

 of the yolk and constitute the endoderm. 



The mesodermic bands arise later by proliferation from the 



