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 odgonia 
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, 
