On tlic varying dümiuaiice of oortain white breeds of the silk-worm, etc. 287 



batioii in the order of inheritance by double mating arc due to the 

 presence of mixed white breeds which were considered as homozygous. 



Concerning the zygotic composition of the dominant white form 

 so far discussed, whether it is due to the presence of some suppressing 

 or inhibiting factors or not, we sliall wait and see the result of our 

 further experiments. 



It is worth noting here, however, that, as far as we are aware, 

 there is no white mating which gives all yellow Fj as in the case of 

 other animals and plants in which white matings sometimes give all 

 coloured F,, and that all the whites derived from yellow matings 

 always behave as recessive towards yellow in their offspring. Suffice 

 it now to say that there are two kinds of Mendelian whites in the 

 silk-worm, the one always behaving as epistatic and the other as 

 hypostatic towards the yellow. When both characteristics come 

 together in one breed, they will produce seemingly contradictory results 

 to Mendelian principles. 



Summary. 



1. In domesticated silk-worms there are, as in other animals and 

 plants, two kinds of white breeds, one dominant towards yellow, 

 pinkish-yellow or other coloured breeds and the other recessive to- 

 wards them. 



2. Occidental whites such as Blanc des Alpes, Petit hlanc Fays, 

 Italian white, Sina blanc, including Bagdad white belong to the 

 dominant, some being a mixture of both antagonistic whites. The 

 majority of Oriental whites, on the contrary, belong to the recessive 

 category. As far as we are aware, there is no record of dominant 

 whites in Japanese or Chinese breeds hitherto investigated. 



3. So called inconsistent results as to dominancy and recessiveness 

 of the white characteristic of cocoons of certain silk-worms which were 

 observed by Coutagne and Kellogg may better be explained as the 

 effect of a mixed breed than considered as due to strain or individual 

 idiosyncrasies. 



4. Kellogg's perturbation in the order of inheritance by double 

 mating seems to us not the effect of double mating but that of a 

 mixture of two different whites in one breed. I quite agree with 

 Castle ('11) who after excepting some minor irregularities says "so far 

 there is encountered nothing at variance with Mendelian expectation". 



