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THE AMERICAN NATURALIST [Vol. LI 



Here then we get an idea of one of the stages through 

 vhich the products of Mendelian genes for hen-feathering 

 their results. The ])resence of these genes withii 



the male birds causes the testes to produce some substance 

 that carried into the body inhibits the full development 

 there of certain feathers. The presence of these genes in 

 the other cells of the body is without influence on the 

 plumage, except in the presence of the testes. The activ- 

 it> of the latter is such that a substance is produced there 

 thnt ha- an inhibitory effect. 



In other words, we are fortunate enough in this case 



