144 MISS MAUDE L. CLEGHORN ON THE INHERITANCE OF 



were deep yellow too ; in other cases, two deepish yellow F 2 

 cocoons produced some flesh-coloured and even white ones. 



I also found that flesh-coloured parent cocoons would, in some 

 cases, give only flesh-coloured ones, ancj in others flesh-coloured 

 and white. 



Table 2 shows that among all the yellows in F 2 there are two 

 kinds — the pure (homozygous) dominants YYff and YYFF and 

 the hybrid (heterozygous) dominants Yyff, YyFF, and YyFf. So 

 when YYff and YYff are chosen as the parents, all the offspring 

 Avill produce deep yellow cocoons, but if YyFF and YyFf are 

 chosen, about a quarter of the cocoons will be flesh-coloured, and 

 if the light yellow Yyff and Yyff are chosen as the parents, about 

 a quarter of the cocoons will be white. 



In his experiments with the white Japanese and yellow 

 Siamese, Toyama obtained from the F 0 yellows some which 

 produce only yellows, and 2 yellow cocoons which gave 221 yellow 

 and 77 pinkish yellow, and 2 yellows which produce 254 yellow 

 and 77 white cocoons. These results obtained by him give almost 

 the exact proportions (75 per cent, and 25 per cent.) I have 

 obtained in my analysis of the colour factors, Diagrams (2) 

 and (3) Table 4. 



Among the flesh-coloured cocoons they are two kinds — the 

 homozygous FFyy and the heterozygous Ffyy. Parent cocoons 

 which are both FFyy will produce all flesh-coloured ones, but 

 two Ffyy parent cocoons will give a few white ones. Table 4, 

 Diagram (3). Toyama appears to have obtained both the pure 

 and impure flesh-coloured cocoons in his experiments. For, 

 referring to them, he states "the pale-pinkish-yellow form pro- 

 duces some uniform (producing only pale-pinkish-yellow) and 

 some mixed (the white 25 per cent, and the pale-pinkish-yellow 

 75 per cent.) offspring in each succeeding generation." 



The pure white cocoon bred inter se always gave white cocoons. 

 The yellowish white cocoons. The yellowish- white ones, how- 

 ever, mostly gave a small percentage of yellow cocoons. 



In the gametes of the pure white cocoons there is no colour 

 factor, so when the parent cocoons are both pure white the 

 offspring inherit only colourless factors and will all be white. 

 Table 4, Diagram (3). 



The white recessives are also easily distinguished from the 

 dominant yellow T s, and as they are pure (homozygous) in the 

 colour character, a race with white cocoons can be easily 

 made from white cocoons which appear in any of the generations. 

 Toyama also found that " every white form from its first pro- 

 duction remains true to itself." 



The recessive character always breeds true in whatever genera- 

 tion it occurs, but as it never is present in the F lS after a cross, 

 the Fj individuals must always be reared, as the recessives make 

 their first appearance in F„. 



On the whole the results of these experiments, excepting that 



