278 The Inheritance of Wing -Colour in Lepidoptera 



that the males of the Fy^ generation were a little darker than rustica. 

 Adkin described the hybrid males as dusky white, and Standfuss, who 

 obtained his pupae from Caradja, bred 17 F^ </(/'> the darkest of which 

 was much lighter than the lightest type. Caradja classified the Fi hybrids 

 under the names of var. standfussi (intermediate between dark grey 

 and milk white), var. mus (darker grey but lighter than type), var. clara 

 (pale dirty yellow), and vai'. mixta (pale as clara, but heavily spotted). 

 Nevertheless, 20 per cent, of the males could not be classified in any 

 of these categories. All these authors, however, agree in finding the 

 -^1 cT </ b^t little darker than those of var. rustica. 



The fullest details are recorded by Cockayne, and he concludes that 

 " the results show no segregation of the dark brown colour of the type 



form takes place, either in F^ or ^5 generations ; even with the small 



numbers bred I think it safe to say that the pale colour of var. rustica, 

 and the dark brown of the type do not behave as Mendelian unit 

 characters." The present writer does not consider that sufficient evi- 

 dence is advanced to justify these conclusions, and, moreover, the 

 experiments recorded later suggest that segregation does take place, 

 though it is partly obscured by modifying genes which tend to make 

 the variation appear continuous. The 46 F^ ^^ recorded by Cockayne 

 vary from creamy brown to the same pale colour as rustica. In the 

 F2 generation, which in the event of segregation should approximately 

 contain 3 pale or buff insects to every black one, only 4 (/*(/ are recorded, 

 and one of these was described as a dark intermediate. Moreover, from 

 the data given, all the F.^ generation came from matings of the form 

 DD X BD or DD x DR (where D stands for the imperfectly dominant 

 factor for rustica. and R for the factor of the recessive black type 

 form). This may be more clearly seen from the pedigree given below. 

 Only two F. broods are recorded, namely (i) and (ii), the male parents of 

 which came from the F.^ generation, and are described as " pale rustica," 

 thereby almost certainly having the constitution DD. The two female 

 parents came from the same Fo, family as the male parents, but being 

 of course white they might have had any constitution, DD, DR or RR. 

 Since, however, the 1\ ^ ^ recorded in brood (i) were as pale or rather 

 paler than rustica (one was said to be like var. mixta), the % must have 

 been DD or at least DR. In brood (ii), 6 of the cfcT recorded were as pale 

 as rustica, and the others (number not mentioned) were a pale creamy 

 brown. The male parent of this brood was, as has been pointed out, DD, 

 and therefore the female parent must have been DR, because the male 

 offspring were, as would be expected, partly riistica and partly buff {DD 



