Facts and Factors of Development 



27 



there is no fundamental difference between oviparity and vivi- 

 parity. In the latter the union between the embryo and the 

 mother is a nutritive but not a protoplasmic one. Blood plasma 

 passes from one to the other by a process of soakage, and the only 

 maternal influences which can affect the developing embryo are 

 such as may be conveyed through the blood plasma and are chiefly 

 nutritive in character/ Careful studies have shown that sup- 



FIG. 12. DIAGRAMS SHOWING THE EARLY DEVELOPMENT OF THE HUMAN 

 OOSPERM. A, cleavage stage which has just come into the uterus; B and 



C, blastodermic vesicles embedded in the mucous membrane of the uterus ; 



D, E and F, longitudinal sections of later stages, the anterior and poster- 

 ior poles being marked by the axis a p. In C cavities have appeared 

 in the ectoderm, endoderm and mesoderm. D, villi forming from the 

 trophoblast (nutritive layer, tr} ; black indicates ectoderm (ect) ; oblique 

 lines, endoderm; few stipples, mesoderm; V, villi; am, amnion; ys, yolk 

 sac; n, neurenteric canal; x 25. (After Keibel.) 



