66 ZOOLOGY 



the specific number of chromosomes at fertilization. 

 The polar bodies perish, and consequently some of the 

 material of inheritance is wasted, but the surviving 

 group of chromosomes carries all the cytoplasm neces- 

 sary for the beginnings of development after fertiliza- 

 tion. Were this cytoplasm divided equally, in a process 

 similar to that which makes two sperm cells, there would 

 probably not be enough for either, and both, though 

 fertilized, would perish. 



The spermatocyte, or sperm-forming cell, divides to 

 form two, and these divide again to form two spermato- 

 zoa each. The oocyte, or egg-forming cell, does not 

 thus divide; but its nucleus divides, so that there re- 

 sults one large cell and a polar body. The large cell 

 undergoes another nuclear division, as described above, 

 when the second polar body is formed and the number 

 of chromosomes is reduced to half. The first polar 

 body also divides, but comes to nothing. Thus, where 

 four spermatozoa are formed, the corresponding cells of 

 the female are one functional egg cell and three minute 

 cells which perish. As a matter of fact the spermatozoa 

 produced by the male are vastly more than four to one 

 egg cell of the female, following the law that the number 

 produced must vary with the chances of survival. The 

 male produces myriads of spermatocytes, and hence 

 vast numbers of spermatozoa. 



When fertilization takes place, each gamete (matured 

 germ cell) brings to the union its half set of chromo- 

 somes, and thus the regular number is made up again. 

 Were it not for this, the number would be altered at 

 each fertilization ; thus, without the reduction division, 

 each gamete would carry the full number typical of the 

 species, and uniting, the two would double the number. 

 After several generations there would be an enormous 



