K. TOYAMA 401 



of temperature during the incubation of the egg, more strictly, during 

 the embryonal stage after sexual cells are liberated from the mesodermal 

 tissue. If we expose eggs at this stage to a temperature of about 

 60 — 65° F. or lower until hatching, all the moths derived from them 

 will lay divoltine whitish eggs; on the contrary, if we subject them to 

 a temperature of 80° F. or more, all the eggs will become univoltine 

 coloured ones. This is a well-known fact among Japanese breeders and 

 has been made use of for industrial purposes for the last twenty years. 



(2) The eggs laid by the second brood of the divoltine breed are identical 

 in appearance with the univoltine eggs and hibernate without hatching. 

 In the case of crossing, we are, therefore, unable to eliminate divoltine 

 characterized eggs from the univoltine in every alternate generation. 



(3) The maternal inheritance referred to above, which also prevents the 

 proper elimination of antagonistic characters. 



These are the causes why, I think, the character " voltinism " behaved 

 so irregularly that McCracken considered it to be non-Mendelian. 

 Generally speaking, I believe, the order of inheritance of the " voltinism " 

 of the silk- worm will follow the course before mentioned in our scheme. 



In a later paper I propose to give a fuller account of the phenomena 

 connected with voltinism. 



Before concluding this paper, I wish to express my sincere thanks 

 to Prof. W. Bateson who has kindly assisted me in many ways when pre- 

 paring this paper for press. Thanks are also due to Mr S. Hashimoto, 

 assistant in our laboratory, who has helped me in rearing the worms 

 used in our experiments since 1906. 



VI. Summary. 



1. In the egg of the silk-worm there are certain special character- 

 istics of shape, colour, etc. which differ in different breeds or even in 

 the same breed. Japanese green breeds generally lay green-shaded eggs 

 varjdng in depth of colour, often mixed with normal coloured ones. 

 Most of the Chinese and European breeds lay similar green-shaded eggs, 

 both of them, however, being distinguishable from each other by special 

 lustres and shades. Eggs of the Japanese normal breeds are, however, 

 brownish slate shaded with some light pink or purple. 



Among the eggs laid by Japanese normal-egged breeds we often find 

 many variants in shape and colour, a smaller number of the variant 

 being sometimes found in a batch, frequently in Mendelian proportions. 



