l6 INHERITANCE IN SILKWORMS, I 



(as in Japanese White X Italian Salmon, and Italian White X Italian 

 Salmon) not only tiger-banded larvse and patterned larvae appear but 

 also tiger-banded-patterned larvae (PI. I, fig. 5) and pure white larvse. 

 And this in the first generation as well as in later ones. In matings of 

 patterned larvse with white ones (race crosses) pattern is regularly 

 dominant, and follows Mendelian proportions. Occasionally a pure 

 white larvae or two appear in a pure Japanese White race lot (pat- 

 terned larvae). For example, in a 1905 pure race crossing of Japanese 

 White, two white (unpatterned larvae) appeared, and these mated to- 

 gether (they were fortunately male and female) produced a lot of 

 uniformly white larvae. 



White type. — White is regularly recessive to all of the other larval 

 color-pattern types. And white larvae mated with white never produce 

 any but white larvae. 



Cocoon Colors. 



The various cocoon colors represented by the races being reared in 

 my laboratory are white, green, pale pinkish yellow (or salmon), lemon 

 yellow, and golden yellow (see Plate IV). To these colors, which are 

 race characteristics, I have added as the result of "break-downs" after 

 hybridizations a long series of mid-shades connecting any pair of 

 members of the racial series. The facts and results of these "break- 

 downs" are to me the most interesting data, perhaps, that the 

 silkworm work has revealed, for I seem to see in them a significance of 

 prime importance. The pointing out of this significance and the facts 

 of the breaking down of the racial color types may be passed for the 

 moment, however, to attend to what phenomena of alternative and 

 Mendelian inheritance may be discovered in these cocoon types. 



Mating gold yellow (Istrian race) with pure white to faintly 

 greenish white (Bagdad race) produces sometimes an all gold-yellow 

 first generation with splitting in Mendelian proportions in the second 

 generation lots as in the following example : 



Fi (^ Istrian (gold-yellow) X $ Bagdad (white) ; produced all 

 gold-yellow cocoons. 



F2 Hyb. yellow X hyb. yellow; produced 64 yellow, 24 white 



cocoons. 

 Fg Hyb. yellow X hyb. yellow; produced 61 yellow, 28 white 

 cocoons. 



But this is not always the result of a gold-yellow X white mating, 

 even using the same races. As an example: 



