108 SEX INHERITANCE 
is produced in the testes of the hen-feathered birds, 
that, acting together with the somatic complex of 
the same bird, inhibits the full cock-feathering. It 
seems probable that an internal secretion is set 
free from the testes that acting in conjunction with 
substances produced in the feather follicles, causes 
the feathers to be like those of the hen, while in the 
absence of this secretion the follicles produce cock- 
feathering. In this case, one of the intermediate 
stages between the gene and the feather is located 
in the testes. It is interesting to note in this con- 
nection that when a hen has her ovary removed 
she also becomes cock-feathered (Goodale). In the 
ovary there are certain cells, called luteal cells, 
that are supposed to produce an internal secretion. 
In the adult of ordinary cocks these cells are absent, 
or rare, while in the testes of the Sebright, and also 
in the testes of another race of hen-feathered birds, 
the Campines, cells are present that look exactly 
like those of the female ovary. It seems plausible 
at least, that the secretion in question is produced 
by these cells and that it produces the same effect 
on the hen and on the hen-feathered male. In the 
Campines the hen-feathered males are recognized 
in some countries as the standard, while in other 
countries cock-feathered males are the standard. 
Here also it appears, although the evidence is less 
certain, that the two races differ by a factor 
for hen-feathering, and here too castration of the 
hen-feathered cockerel causes him to develop the 
cock-feathering like that of the other race. 
