On the varying dominance oi certain whitL- breeds of the silk-worm, etc. 255 



In accordance with my former results ('06), all matings between 

 Japanese or Chinese whites and Japanese or European yellows gave, 

 with no exception, all yellow Fi broods which paired inter se, segregated 

 into white and yellow in F2. Of all F2 broods derived from 30 

 reciprocal matings 2,379 worms spun white cocoons and 7,245 yeUows, 

 a close approximation to a 3:1 proportion. Fj yellows back-crossed 

 with pure whites gave, on the contrary, both yellows and whites in 

 an approximate proportion of 1:1. 



Thus the whites used in this series of experiments behaved as 

 recessive towards Japanese or European yellows. 



The Fl yellow is however not always the same in colour as in 

 their parental yellow, sometimes it is slightly diluted or modified. 

 Of the F2 yellows or whites we also find certain variations of colour 

 as was already noted by Coutagne ('02) and Kellogg {'08). The 

 variations, however, are small and do not cUsturb the distinction 

 between yellow and white cocoons and we are able to separate them 

 with perfect accuracy. Such slight variations may often be obser\-ed 

 in their parental forms. 



There is another characteristic which separates white cocooners 

 from yellows, namely: the colour of the blood. In those which spin 

 yeUow cocoons, the colour of the blood is always deep yellow, while it 

 remains nearly colourless in white cocooners. It may be seen through 

 the thin skin of worms, the colour being especially intense on the 

 inside of the abdominal legs. So if we examine the colour of the 

 feet, we can easily and exactly distinguish the coloured cocooners 

 from the white. 



Japanese, European, Siamese and some Chinese yellows used in 

 our experiments belonged to yellow-blooded breeds, while Japanese, 

 Korean greens and some Japanese greenish yellow such as '''Dainyorai''' 

 belonged to white-blooded races. The wild mulberry silk-worm, 

 Tlieophyla mandarina, M. comes in the same category. 



As far as we experimented, the yellow- and white-blooded 

 characteristics are Mendelian allelomorphs and are always correlated 

 with the colour of the cocoons, the yellow-blooded larvae always 

 spun yellow, flesh-coloured or some other coloured cocoons, and the 

 white ones white or faintly shaded cocoons. 



Present experiments are only concerned with yellow-blooded 

 breeds, because breeds used by Coutagne and Kellogg are mostly 

 yellow-blooded. The order of inheritance of the white- blooded breeds 

 which spun coloured cocoons such as green, greenish yellow, canary 



