ALICE M. BORING AND T. H. MORGAN 131 



in the Sebright. These factor-differences produce their effects 

 through the testes. The presence of these genetic factors, we now see, 

 causes the testes of the Sebright to produce a kind of secretory cell 

 that is ordinarily only produced in the female, or possibly to a slight 

 extent in young males (Boring), or in numbers insufficient to sup- 

 press the male plumage in the testes of some ordinary cock birds 

 (ReevesO • 



. ^Reeves, T. B., Anat. Rec, 1915, ix, 383. 



