128 THE STORY OF LIFE'S MECHANISM. 



interest to have this settled, for if it should 

 prove true, then it would evidently follow that 

 the machinery for cell division, in the case of 

 sexual reproduction, is derived from the father, 

 although the bulk of the cell comes from the 

 mother, while the chromosomes come from both 

 parents. 



In the cases where the process has been most 

 carefully studied, the further changes are as 

 follows: The head of the spermatozoon, after 

 entrance into the egg, lies dormant until the egg 



FIG. 41. Fiu. 42. 



FIG. 41. The chromosomes in the male and female pronucleii have 

 resolved into a network. The male centrosome begins to show 

 signs of activity. 



FIG. 42. The centrosome has divided, and the two pronucleii have 

 been brought together. The network in each nucleus has again 

 resolved itself into two chromosomes which are now brought 

 together near the centre of the egg but do not fuse; mcr, repre- 

 Bents the chromosomes from the male nucleus ; /cr, the chromo- 

 somes from the female nucleus. 



has thrown off its polar cells, and thus gotten rid 

 of part of its chromosomes. Close to it lies its 

 centrosomes (Fig. 35, ce\ and there is thus 

 formed what is known as the male pronudeus 

 (Fig. 35-40, mri). The remains of the egg 

 nucleus, after having discharged the polar cells, 



