550 GENETICS IN RELATION TO AGRICULTURE 
In birds some striking results of castration have been obtained. 
Goodale especially has made extensive investigations with ducks and 
fowls. The results of ovariotomy in Rouen ducks are shown in Plate IV. 
Early removal of the ovary results in almost complete assumption by 
the female of the strikingly different plumage patterns of the male, and 
along with them of other secondary sexual characters peculiar to males. 
If removal be later or incomplete, the assumption of male secondary 
characters is correspondingly less complete. Castration of the drake on 
the other hand has very little effect on the secondary sexual characters. 
Here if any change in characters occurs, it is toward the infantile condition 
rather than toward that of the opposite sex. Observations on Brown 
Leghorn fowls confirm these conclusions. Thus an early ovariotomized 
female developed almost a complete set of male secondary characters. 
Capons, on the other hand, exhibited almost the entire set of male sec- 
ondary characters. The characters of such birds, which are responsible 
for the current belief that capons are feminized cocks, were shown to be 
infantile characters rather than characters of the female sex. 
Finally, mention must be made of Steinach’s experiments on guinea- 
pigs and rats. Steinach first castrated male guinea-pigs and rats and 
then transplanted ovaries into them. The animals thus operated upon 
became strongly feminized. Feminized rats took on the texture of hair, 
the size of skeleton, and sexual behavior of females. In both cases 
the mammary glands became greatly enlarged. Throughout the total 
changes wrought by the establishment of ovaries in the castrated male 
rats and guinea-pigs were such as to throw the whole set of developmental 
processes toward the female side. We await with interest further ex- 
periments of this kind. 
We can only conclude from these experiments that the sex glands 
actually furnish something, in the way of internal secretions perhaps, 
which affect the internal conditions under which the cells react. The 
presence of these hormones is the exciting condition for development 
of secondary sexual characters, not any fundamental factor difference 
in the two sexes, save that of the sex-determining factor itself. This, as 
Lillie has shown, is the most reasonable explanation of barrenness in 
free-martins. Inmammals the effect of castration on the male is to throw 
the secondary sexual characters toward the female side, but not very 
strongly. The effect is only complete when ovaries are present. The 
female, however, is little affected. In birds the relations are reversed, 
castration of the female leads to the development of the secondary 
sexual characters of the male; castration of the male to little change. 
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