Toyama, Mendel'* laws of heredity a.s applied to the silk-wörm crosses. 325 



generation, when thc yellow forms derived from Group (D) were 

 bred together. 



In the third generation we have missed that niixed form con- 

 sisting of fonr different kinds of worms, which is probably due to 

 the scarcity of worms reared. 



It will be not uninteresting to mention here that of the mixed 

 offspring consisting of yellow (74,24 %) an d ^ esn coloured (25,75 °/ ), we 

 learn, after three generations experiments, that the relation between 

 the yellow and the flesh is quite similar to that of yellow and 

 white, the yellow being dominant and the flesh recessive in 

 Mendel's sense. 



3. The flesh-coloured form. When mated together, the segre- 

 gation of the parent-characters into white and flesh took place in 

 the proportion of the first 25,2 °/ and the second 74,7%- Their 

 posterity behaved exactly like the white X yellow in simpler cases 

 before mentioned. 



4. The greenish white form. With this form, we also observed 

 the segregation of white and greenish white forms. We have 

 abstained however, from calculating their nnmbers, since it is 

 difficult to separate dirty white cocoons and light greenish white 

 ones. We have good reason to believe, however, that they will 

 display similar phenomena of heredity as those forms above enu- 

 merated. 



The following table will give a clear conception as regards 

 the mutual relations between these fonr forms. 



It will probably snffice to say now that every phenomenon 

 displayed by these crosses dnring six generations accords very well 

 with Mendel's law of mono- and dihybrids. 



C. Offspring of cross-breds when crossed with one of the original forms. 



When cross-bred yellow forms in the fourth generation of the 

 Siamese "whites" X Siamese "yellows" were crossed with the 

 original white forms or Siamese "whites", some of them produced 

 uniform yellow offspring while others both yellow and white in the 

 proportion 821 : 825 or nearly 1:1. 



In the second generation when each of the yellow forms we 

 paired inter se it splits up into white (24,52 °/ ) and yellow (75,47 °/ ). 



On the contrary, when -it is crossed with original yellows or 

 Siamese "yellows" it gave uniform yellow offspring through two 

 generations. 



The results above quoted may be explained after the Mendel - 

 ian law. As the cross bred yellow forms in the fourth generation 

 are D or DR, as already stated, the crossing with "whites" or R 

 will produce: D X R = hybrid yellow or (D -\- R) R = yellow 

 50°/ -\- white 50°/ . In the second generation, therefore, all the 



