324 Toyama, Mendel's laws of heredity as applied to the silk-worm crosses. 



hybrid dominani or DR. Now since in our case there is no means 

 of distinguishing pure yellow (= pure dominant) froni hybrid one, 

 the crossing of these forms at random is the necessary result and 

 we may reasonably expect to get three combinations, D X D, DR X D 

 and DR X DR. In the former two combinations, all offspring ex- 

 hibit the dominant character, while one of them (DR X DR), when 

 mated together, will produce mixed offspring. This may serve to 

 illustrate the first discrepancy above cited. 



Similarly, from random mating within the forms D and DR, 

 it will not be expected be produeed D X D and DR X D in a con- 

 stant proportion, which may explain the second of the discrepancies 

 under discussion. 



B. Coraplex cases. 

 The first cross generation. 



In crossing Japanese "whites" with Siamese "yellows" or 

 Japanese "whites" with European "yellows" the first generation 

 gives always yellow offsprings as usual. 



The second cross generation. 



When these yellow forms are paired inter se, there are produeed 

 four kinds of cocoons, 1. pure yellow, 2. pale-pinkish-yellow or 

 flesh-coloured, 3. greenish white and 4. pure white, the proportion 

 in each mating being yellow 70: flesh 21: greenish white 24: pure 

 white 12: which eoineide fairly well with what we expect aecor- 

 ding to Mendel's law, i. e., yellow 72: flesh 24: greenish white 

 24: pure white 8. 



The third generation. 



Of these four forms mated like with like, we have observed 

 very interesting phenomena of the segregation of the colours, which 

 will be described as follows: 



1. The pure white form. This is constant from its very first 

 appearance. As far as our experiments go, we have never observed 

 even a single case of coloured ones among its offspring. 



2. The yellow form. This form displays phenomena of segre- 

 gation and combination of various forms which are far more com- 

 plex and interesting. 



Of 10 parents mated with similars, (A) one parent produeed 

 the uniform yellow offspring, (B) four parents mixed offspring 

 of white (23,35 °/ ) and yellow (76,64 °/ ), (C) two parents mixed 

 • »lispring of yellow (74,24 °/ ) and flesh coloured (25,75%) and (D) 

 the rest a mixture of four forms, white and greenish white (23,98 °/ ), 

 yellow (56,43 °/ ), and flesh coloured (19,57°/ ). 



Quite a similar phenomenon has been observed in the next 



