16 
SIDNEY I. KORNHAUSER 
coverings of twin embryos of opposite sex fused so that the blood 
vessels anastomosed, the more rapidly developing male embryo 
sent out hormones into the common circulation which inhibited 
the normal development of the female embryo. The much 
modified female embryo might then be born as a freemartin. 
Even the ovaries show considerable alteration and tend to form 
tubules quite like those of a testis. 
In birds the activity of the gonads likewise controls to a large 
extent the development of secondary sexual characteristics. 
Black Male Barred Female 
Z Z Z 0 
G-ametes and Combinations “ 
Z* Z 
^ z Z 0 
Barred Males Black Females 
Gametes and Combinations 
Z 
(1) Males (2) 
Z Z Z Z 
Barred Black 
(3) Females (4) 
Z 0 Z 0 
Barred Black 
Fig. 8. Diagram Showing Cross Reciprocal to that Shown in Figure 7 
This has been nicely demonstrated by Goodale and Morgan in 
castration and transplantation experiments on ducks and fowls. 
Most striking is the case of female birds, which, when castrated 
while still young, develop the male plumage and posture. 
The whole problem of sex hormones is very complicated, for 
it has been shown that the secretion of the gonads is merely one 
link in the chain of factors, and that other endocrine glands con- 
tribute to form a complex of factors, which controls to a large 
extent the expression of the genes for the secondary sexual 
