The Cellular Basis 161 



as in the game of "bean porridge" there will be an equal number 

 of cases in which a hand with five digits meets one with five 

 (female) and one with four meets one with five (male). In the 

 latter case there will be an "odd" thumb (chromosome) which 

 has no mate. 



Sex Determination in Man. — Even in man sex is determined in 

 the same manner, according to several recent investigators. There 

 are in the spermatogonia of man 47 chromosomes, according to 

 Winiwarter, one of which is the X or accessory chromosome 

 (Fig. 56 A.) These unite in synapsis into 23 pairs, leaving the 

 X chromosome unpaired (Fig. 56 B) and in the reduction di- 

 vision the pairs separate, while the X chromosome goes entire 

 into one of the daughter cells, which consequently contains 

 23 -f" X chromosomes, whereas the other daughter cell con- 

 tains 2$ chromosomes (Fig. 56 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 chro- 

 mosomes, according to Winiwarter, there being two X chromo- 

 somes, one from each parent, and after the reduction divisions 

 every egg contains 24 chromosomes. If an egg is fertilized by 

 a sperm containing 24 chromosomes an individual with 48 chro- 

 mosomes, or a female, is produced; if fertilized by a sperm with 

 23 chromosomes an individual with 47 chromosomes, or a male, 

 results (Fig. 56). 



It is a curious fact that it has been very difficult to determine 

 the exact number of chromosomes in man. This is probably due 

 to the difficulty of preserving in an unaltered condition the chro- 

 mosomes of mammals in general, as McClung and his pupils have 

 shown, and also to the peculiar difficulty of obtaining human tis- 

 sues in a perfectly fresh and normal condition. Thus Guyer and 

 Montgomery have not found 47 chromosomes in the spermato- 

 gonia of man, but about 22. Since both the latter investigators 

 worked on negroes whereas Winiwarter worked on white men it 

 has been suggested by Morgan and Guyer that there may be 

 twice as many chromosomes in the white race as in the black. 



