292 The Inheritance of Wing-Colour in Lepidoptera 



of distribution curves in the manner previously described enables the 

 segregation of these variable insects to be followed without difficulty. 



4. Segregation is found to take place in the F^ generation, the pure 

 rustica and the black type males segregating from the heterozygous 

 buff coloured insects in an approximately 1:2:1 ratio. Owing to the 

 fact that some heterozygous males are indistinguishable from pure rustica, 

 the latter class is found to be too numerous. 



5. The crosses between the F^ generation and type individuals also 

 show very clear segregation in the males, there being equal numbers of 

 type, and buff coloured or white insects. 



6. The statement that var. rustica is phylogenetically the older 

 race is supported by a consideration of what is known concerning the 

 chemistry of black pigments. 



I have to acknowledge my thanks to the British Association for 

 defraying part of the expenses of this research by a grant of £25 during 

 the year 1920, and I am also indebted to Professor Punnett for reading 

 the manuscript. I am particularly gi'ateful to Miss Helen Moodie for 

 her care of the larvae and for her efforts to prevent the spread of infection 

 while changing the food. 



DESCRIPTION OF PLATE XXVII. 



Diaphora mendica, var. rtistica and hybrids. Natural size. 



1. D. mendica. Typical wild English ^ from Kent. 



2. D. mendica. Black type F^,^, extracted from var. standfussi {Fi). 



3. Var. standfussi. Dark F^ ^ from cross mendica x rustica, showing pale central areas 



on fore wings. 

 Note the pale colour of the thorax and abdomen, a sure indication that the insect is 

 heterozygous. 

 4, 5. Var. standfussi. Dark Fi ^ ^ from cross mendica x rustica. 



6. Var. standfussi. ^ from cross Fi x type, showing pale veining. 



7. Var. standfussi. Fj ^ from cross mendica x rustica. 



The colour of this insect, or a little darker, is about the usual shade oi Fi^ ^. 



8. Var. standfusn. J from cross rustica x Fi , showing patches of grey scales, which are 



not as a rule so dark. 



9. Var. rustica. Typical white Irish ^J. 



10. Var. rustica. White Irish ^ , showing black streak on costa. 



11. Var. rustica. Irish $ , showing black costa which appears in certain families, in 



which the black spots are often rather heavier than usual. 



12. D. mendica. Typically English 9 from Kent. 



