On the varying dominance of certain white 

 breeds of the silk-worm, Bombyx mori, L. 



By K. Toyama. 



(Zoological Institute, College of Agriculture. Tokyo Imperial University.) 



As to the inheritance of white breeds of the silk-worm, the 

 results obtained by Coutagne ('02) and the writer ('06) do not accord 

 well. While the white breeds (Japanese, Chinese and Siamese whites) 

 studied by the writer were all hypostatic to the yellow, those observed 

 by Coutagne (Blanc des Alpes, Petit blanc Pays, and Bagdad ivhite} 

 were mostly epistatic to the yellow. Moreover, he observed and 

 clearly described that in certain cases yellow dominates over white 

 in part of the zygotes only, and in the remainder white dominates 

 over yeUow, that is to sa}', the dominance is not uniform. 



Quite similar results were obtained by Kellogg ('08) who crossed 

 Bagdad white with Istrian yellow, Italian Salmon or French yellow. 



As to the cause of the varying dominance of the white, nothing 

 definite is, however, as yet known. 



The results of experiments made by the writer during the last 

 few years in the Zoological Institute of our College may, I think, 

 throw some light on the question. They will be described in the 

 following pages. 



We shall first describe the results of crossing between Japanese 

 or Chinese whites and European or Japanese yellows. 



White breeds used for the present experiments are: tetravoltine 

 (Tatsutahimc and Onodahime), divoltine (CliTisic, and Hakiirin) and uni- 

 voltine whites (Japanese whites : Datenishiki, Chinese whites : Spotted 

 and Orarige-egged breeds). 



YeUow breeds: "Papillons noirs", "I'ar" and Japanese tetravoltine 

 yeUow called "Onodahime", the first two being the same breeds studied 

 by Coutagne. 



The results of reciprocal crosses between these breeds are 

 tabulated below: • — 



