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Y. TANAKA. 
side of the question, Prof. Toyama being, as far as I am aware, the only- 
author who explained his results by Mendelian factors. Generally speaking, 
however, his system of analysis seems to have been based on tne original 
view of Mendel, who considered that “there was a factor corresponding to 
the dominant character and another factor corresponding to the recessive 
character of each alternative pair of unit-characters, and the characters were 
alternative because no gamete could carry more than one of the two factors 
belonging to the alternative pair”. (Punnet, 1911, p. 28.) 
In the following page I shall quote the experimental results of Prof. 
Toyama and other authors and try to show that they can be interpreted 
with no difficulty on a more recent hypothesis, the presence and absence 
hypothesis, now generally accepted by students of genetics. 
By the way it may be noted here that I have been also engaging upon 
a series of hybridization experiments with the silkworm during the last few 
years and that the results so far obtained, differing greatly at some points 
from what has been reported by the above-named investigators, will be 
described in another paper in this journal. 
Toyama’s Results and His Factors. 
In a paper published in 1906 dealing with the inheritance of larval 
markings, cocoon colours, and other characters in the silkworm, Prof. Toyama 
uses in the case of monohybridism symbols D and R to denote a dominant 
and a recessive character respectively, while in the case of dihybridism he 
assumes a factor for each character. On this assumption all the cases were 
explained without difficulty. But he met with two complex cases which he 
describes as “modified dihybrids”. 
1. First example of the “modified dibybrids”. 
In a cross, Japanese white £ x Siamese yellow he obtained uniform 
yellow-cocooners in F„ which consisted of the following four classes behaving 
differently in production of F 2 offspring. 
