MEDELIAN FACTORS IN THE SILKWORM. 
93 
Fi 
Class 1. 
f 2 
Yellow only. 
” 2. 3 yellow : 1 white. 
” 3. 3 yellow : 1 salmon 11 . 
” 4. 9 yellow : 3 salmon : 4 greenish white 
to pure white. 
The yellows of the fourth class consisted again of four categories, a certain 
of which splitting in F :i into three forms, yellow, salmon and greenish 
to pure white in the ratio given above. But as regards how such a 
remarkable case of Mendelian inheritance is brought about, Prof. Toyama 
offers no interpretation. 
2„ Second example of the “modified dihybrids”. 
The cross between Japanese common white females and Siamese zebra 1 2) 3 
white males produced in Fj in some cases (1) only zebra-patterned, in other 
cases (2) zebra and common in equal numbers, and in still other cases (3) zebra, 
common and plain 31 in the ratio 2: 1 : 1. Zebras of the first class, when inbred, 
yielded 'three F 2 forms in the proportion of 12 zebra: 3 common : 1 plain. 
Here Toyama assumes that there exist three definite factors, namely : 
Zebra-ness (S), Commonness (C), Plainness (If), 
the parental cross being : 
(C + N) X (S + N). 
He remarks : “In this combination, we take for granted that both the 
characters in the parenthesis sometimes act as a whole character, sometimes 
as separate characters”. Thus in cases the gametic combination takes place 
in the following fashion : 
'C + N' x (S + N) = SC + SN + CN + N, 
F, individuals produced will consist of zebra, common and plain, represent- 
ing the third of the above-mentioned three classes. If, on the other hand, 
C + N ) and S + N j simply combine together as such, then Fi offspring 
will consist of zebras only and represent the first class. These zebras, when 
1) “Pale-pinkish -yellow” as he calls. 
2) “Striped” according to his expression. 
3) “Pale” as he designates. 
