REVIEW OF BIOLOGY OF SEX-DETERMINATION 
15 
of normal males. In cattle and horses the individuals are 
docile compared with the fiery males. They lack the thick neck 
and put on fat more readily than males. In man, the voice 
fails to change, the epiphyses of the bones fail to fuse, the beard 
is weak, and the spirit dulled. Females deprived of ovaries 
early in life fail to develop normal mammary glands, and the 
skeletal characteristics likewise are much altered. Extensive 
experiments have proved that in birds and mammals secretions 
Barred Male 
Z I 
Black Female 
Z 0 
Gametes and Combinations 
Z Z 
Z 0 
S z 
Barred Males 
Z 0 
Barred Females 
Gametes and Combinations 
ps 
U) Males (2) (3) Females (4) 
Z2 ZZ ZO ZO 
Barred Barred Barred Black 
Fig. 7. Diagram Showing Sex-Linked Inheritance in Poultry 
An underscored Z indicates the presence of the gene for barring; because this 
is a dominant gene, any individual with an underscored Z will be barred. 
of the gonads are essential to normal development. , The castra- 
tion of young male rats followed by the ingrafting of ovaries 
causes these individuals to be feminized. They develop mam- 
mary glands, have female characteristics of skeleton and hair 
pattern, and also possess female sexual instincts. 
Perhaps no better case of hormone influence is known than 
that of the freemartin, adequately explained through the observa- 
tions of Lillie. He found that in cattle, when the chorionic 
