THE CELLULAR BASIS 145 



type of spermatozoon which enters the egg 

 (Fig. 36). 



Even in man sex is determined in the same 

 manner, according to several recent investi- 

 gators. There are in the spermatogonia of 

 man 47 chromosomes, according to Winiwar- 

 ter, one of which is the X or accessory chromo- 

 some (Fig. 37 A). These unite in synapsis 

 into 23 pairs, leaving the X chromosome un- 

 paired (Fig. 37, B) and in the reduction 

 division the pairs separate, while the X chro- 

 mosome goes entire into one of the daughter 

 cells, which consequently contains 23 + X 

 chromosomes, whereas the other daughter cell 

 contains 23 chromosomes (Fig. 37 C and D). 

 The former gives rise to spermatozoa with 24 

 chromosomes, the latter to spermatozoa with 

 23 chromosomes. In the female there are 

 probably 48 chromosomes, according to Wini- 

 warter, there being two X chromosomes, one 

 from each parent, and after the reduction di- 

 visions every egg contains 24 chromosomes. If 

 an egg is fertilized by a sperm containing 24 

 chromosomes an individual with 48 chromo- 

 somes, or a female, is produced; if fertilized 



