272 GERM-CELL CYCLE IN ANIMALS 



chromosomes is reduced in the first division, resulting 

 in two secondary spermatocytes each with eight 

 large ordinary chromosomes, and one large and one 

 small sex-chromosome. During the second division 

 the small sex-chromosome does not divide, but passes 

 intact into one spermatid ; thus two sorts of sperma- 

 tozoa are formed, one with eight large ordinary and 

 one sex chromosome and the others with eight 

 large ordinary chromosomes and two large sex- 

 chromosomes. The spermatozoa with only one 

 sex chromosome is not functional. The oogonia 

 differ from the spermatogonia and somatic cells in 

 the possession of sixteen large ordinary chromosomes 

 and four small sex-chromosomes ; two of the latter 

 arise by the diminution of the chromatin in two of 

 the large sex-chromosomes. The maturation divi- 

 sions are of the usual sort, and all of the eggs are 

 alike, containing eight large ordinary chromosomes 

 and two small sex-chromosomes. Fertilization, as 

 indicated in Fig. 74, always results in a zygote with 

 sixteen large ordinary chromosomes, two large sex- 

 chromosomes, and two small sex-chromosomes, which 

 develop into a hermaphroditic individual. 



Although we know very little about the chromo- 

 somes of man, the data available seem to indicate 

 that here also there are chromatin bodies concerned 

 with sex-determination. The following table indi- 

 cates the state of our knowledge at the present time. 



Guyer (1910) was the first to announce the dis- 

 covery of accessory chromosomes in man. He found 

 twenty-two chromosomes in the spermatogonia. 



