THE CELLULAR BASIS 151 



whereas all ova have this element, and in this 

 case also sex is probably determined by the 

 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. 37-4). 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 



