REPRODUCTION IN MAN 89 



The second important fundamental fact is the 

 elaborate care that nature exercises in arranging 

 that the ovum must pass through a preparatory 

 stage of development before fertilization can take 

 place. During this stage, the same orderly pro- 

 cess of removing chromatin from the nucleus of 

 the human ovum occurs as in animals (page 79). 

 Sperm cells, on the other hand, pass through a 

 series of changes which results in differentiating 

 the sperms into two classes: those that contain 23 

 chromosomes and those that have 24. 



There is no choice on the part of man in the 

 formation and preparation of sperm cells with 23 

 chromosomes, or of those with 24. Each one re- 

 ceives the same essential equipment, although but 

 a few of the hundreds of thousands may ever par- 

 ticipate in giving rise to a new human being. As 

 each ovum is fertilized by but a single sperm, the 

 proportionate number of sperms that ever play the 

 part for which they are grown is very small. The 

 significance of this statement can be made clearer 

 by placing the number of children In a family as 

 the numerator and the estim.ated number of sperms 

 as the denominator of a fraction. 



The only structure that the father contributes is 

 the sperm. After the sperm cell has made its way 

 through the uterine passage and come in contact 

 with the ovum, the tail is lost and the head only 

 enters the egg. Again consulting Fig. 30, it is 

 seen that the sperm-head becomes transformed 



