ONTOGENESIS 



157 



P.O.* 



f 



k 



FIG. 61. Diagrams illustrating the maturation, zygosis, and cleav- 

 age of an animal egg. The primordial germ-cell is represented as possess- 

 ing four chromosomes. (Hegner.) 



its cell genealogy, so to speak back to the unicel- 

 lular -zygote, and since the chromatin of the nucleus 

 of the zygote is derived, half from one gamete and 



