On the zygotic constitution of dominant 
and recessive whites in the silk-worm, 
Bombyx mori, L. 
By K. Toyama and S. Mori. 
(Eingegangen: 13. April 1913.) 
In a paper entitled ‘On the varying dominance of certain white 
breeds of the silk-worm” which was published in Heft 3 and 4, 
Bd. VII of this journal, Toyama (13b, c) advanced the opinion 
that there are two kinds of white breeds in the silk-worm, one being 
dominant and the other recessive towards coloured breeds, such as 
yellow, green etc. In certain breeds, both antagonistic whites are 
mixed. ToyaAMA attributed this (i. e. the mixture of antagonistic 
whites) to the cause of the varying dominance of certain white breeds 
observed by Coutagne and Kellogg. As to the zygotic constitution 
of these breeds, he refrained from drawing any conclusion, pending 
the results of experiments. 
The results obtained from the crossing between Japanese and 
European whites now enable us to draw certain conclusions respecting 
the zygotic constitution of dominant and recessive whites. 
In the spring of ıgII, we crossed females of the Japanese divol- 
tine white (Yamato-nishiki) with males of the European white (sina 
blanc) both of them being white cocooners. The latter white, however, 
as ToyAMA has already shown, is not a homozygous white, for while 
some strains produced all white cocooners others gave both white 
and yellow cocooners in certain proportions. In the present crossing, 
we selected males derived from the strain which gave us all white 
cocooners in the former generation. 
As to the colour of cocoons, that of the Japanese breed is white, 
a few of them being sometimes very slightly shaded with a greenish 
yellow. That of the European breed is also white, but the shade of 
greenish yellow or green is slightly deeper than that of the Japanese 
breed; both of them, however, are practically white and breed true 
to parents. 
Induktive Abstammungs- und Vererbungslehre. X. 16 
