THE CELL AND PROTOPLASM. 109 



tained alone to direct the further activities (Fig. 

 41). Possibly this may be the case in all eggs, but 

 it is not sure. It is a matter of some little inter- 

 est 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 reproduc- 

 tion, is derived from the father, although the bulk 

 of the cell comes from the mother, while the chro- 

 mosomes come from both parents. 



In the cases where the process has been most 

 carefully studied, the further changes are as fol- 

 lows : The head of the spermatozoon, after en- 

 trance into the egg, lies dormant until the egg has 

 thrown off its polar cells, and thus gotten rid of 

 part of its chromosomes. Close to it lies its cen- 



FIG. 41. FIG. 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, represents the chromosomes from the male nucleus ; fcr^ 

 the chromosomes from the female nucleus. 



trosomes (Fig. 35, ce], and there is thus formed 

 what is known as the male pronucleus (Fig. 35-40, 



