B 



Figure 30. This diagram shows in outline merely a few of 

 the more important changes through which the sperm-head, the 

 nucleus of the sperm cell, passes after it enters the ovum in 

 fertilization. Only two chromosomes are shown in F, when there 

 actually are 24 in man. A. Sperm-head in red just penetrating 

 the ovum. B. The ovum nucleus is blue. At this stage the 

 sperm-head is moving toward the ovum-nucleus accompanied by 

 an aster (not discussed in text). C. The chromatin in the red 

 sperm-head has changed into two chromosomes, the full number 

 being 24, and the aster is double. D, E. The chromosomes in the 

 sperm-nucleus have become transformed into a chromatin network 

 with an increase in size of the whole nucleus. The sperm-nucleus 

 and ovum-nucleus now look very much alike. The asters have 

 spread apart. F. The chromatin network has assembled into two 

 chromosomes in each nucleus. G. The nuclear membranes have 

 dissolved and the fibers between the aster increased in number. 

 Each chromosome has divided and one-half will be drawn by the 

 fibers into each of the two cells that are forming. Between the 

 stages F and G there is a union of the male and female chromo- 

 somes which is fertilization. 



