VARIATIONS IN POTENCY 



Relative potency would, therefore, seem to be 

 a character inherited in Mendelian fashion. 1 



Observations of Coutagne on silk-moths may 

 be cited in support of this idea. Coutagne 

 made crosses between races of silk-moths dif- 

 fering in cocoon color, viz. between a race which 

 spun yellow cocoons and another one which 

 spun white cocoons. He found that some of 

 the F! offspring spun yellow cocoons, others 

 white ones. The F yellow cocooned animals 

 when bred together produced F 2 progeny which 

 spun some yellow, others white cocoons, the 

 two sorts being as 3:1. In other words, yel- 

 low in such cases behaved consistently as a 

 dominant character. And the white-cocooned 

 F 5 moths produced in F 2 cocoons of both colors, 

 but in this case the white cocoons were to the 

 yellow ones as 3:1. In other words, when 

 yellow behaved as a dominant in F x it behaved 

 as a dominant also in F 2 ; and the same was 

 true of white. Each retained throughout the 

 two generations the relative potency with which 



1 It is of course possible to interpret such a case as due to the 

 separate inheritance of a factor which inhibits the development 

 of the character, but it is doubtful whether this line of explana- 

 tion can be successfully applied to cases presently to be described. 



