976 THE PHYSIOLOGY OF REPRODUCTION. 



maturation essentially similar to that described for the ovum. 

 Two cell divisions take place with the formation of four spermato- 

 zoa, each of which, however, is a functional spermatozoon. In the 

 process of division the number of chromosomes in each cell is 

 reduced to half part of maternal and part of paternal origin. 

 When the matured ovum and the matured spermatozoon fuse, 

 therefore, each brings half the normal number of chromosomes, 

 and the resulting fertilized ovum is a cell with its chromosomes 

 restored to their usual number. The chromosomes are believed to 

 contain the material which conveys hereditary characteristics. 

 The chromosomes of maternal origin contain carriers of charac- 

 teristics belonging to the stock of the mother, and the paternal 

 chromosomes the carriers for the qualities transmitted through 

 the paternal side. The process which causes each element to lose 

 a part of this material before its union with the cell of the oppo- 



Ovarian egg. 



First polar oody 



Mature egg * 4 Abortive ova resulting 



from division of first 

 polar body. 



Second polar body (abortive ovum). 

 Fig. 304. Schema to indicate the process of maturation of the ovum. (Boveri.) 



site sex is, from this standpoint, a provision by means of which 

 the fertilized egg, from which the offspring develops, shall inherit 

 the characteristics of the stock to which each parent belongs, 

 without increase in the typical number of the chromosomes.* 



Fertilization of the Ovum. The spermatozoon comes into 

 contact with the ovum probably at the beginning of the Fallopian 

 tubes. The meeting of the two cells is possibly not simply a matter 

 of accidental contact, although the number of spermatozoa dis- 

 charged by the male at coitus is so great that there would seem 

 to be little chance for the ovum to fail to meet some of them. Ex- 

 periments upon the reproductive elements of plants indicate, how- 

 ever, that the egg may contain substances which serve to attract 

 the spermatozoon, within a certain radius, by that force which 

 is described under the name of chemotaxis. However this may be, 

 the egg unites with a spermatozoon and under normal conditions 

 with only one. A number of the spermatozoa may penetrate 



* For a popular presentation see Boveri, "Das Problem der Befruchtung," 

 Jena, 1902, and Conklin, loc. ciL 



