\ 



\ 



t 



1 



2 







\ 



II 

 H 



6 



FIG. 73. FERTILIZATION. 



(1) The spermatozoon invades the ovum. (2) The head of the spermatozoon 

 becomes the male nucleus ; radiation appears in the centrosome. (3) and (4) The 

 centrosome has divided ; both nuclei are close together in the centre of the ovum. 

 (5) The chromatin of the nuclei has closed up and become the chromosome. 

 6) Beginning of the development. 



