136 The Inheritance of Wing -Colour in Lepidoptera 



table, p. 124), the character cannot appear in the type offspring, even 

 if the necessary factors were present, becuase radiation is essentially a 

 variation oivarleyata, and could not show on the grossulariata pattern. 



It would seem as if the white radii ought to be a remnant of the 

 dominant white ground of grossulariata, which shows through the black 

 of varleyata, and therefore the radiated varieties should be dominant to 

 varleyata. Inspection of the last table, however, shows that in family 

 18 / one radiated insect was bred from two varleyata parents, but even 

 if this radiated insect is accounted for, by supposing it to have been 

 introduced accidentally like the single grossulariata in the same family, 

 it is seen that the black parents of all the other radiated insects are 

 normal. Supposing radiation to be dominant the grossulariata parents 

 would have to be heterozygous for the factor, in which case the ratio 

 between radiated and non-radiated varleyata should have been one of 

 equality, whereas it is 43 radiated to 140 non-radiated. 



From the scanty data in the last table it is impossible at present to 

 determine the inheritance of this variation with any certainty, but the 

 fact that there is in Abraxas a factor linked to maleness, as well as one 

 linked to femaleness (lacticolor-), is of some interest, for, except in 

 Drosophila this has not been recorded. Suppose in the first place it is 

 assumed that the case is as simple as possible, the factor for radiation 

 being sex-linked to the male, and recessive to varleyata. Then if both 

 parents are heterozygous for the recessive factor, considering the melanic 

 offspring, which alone can show the radiation, there should be one 

 radiated male, one normal male and two normal females, or 4575 radiated 

 to 137"25 non-radiated. This does not differ much from the ratio actually 

 found, which was 43 radiated to 140 non-radiated. The suggestion, 

 however, takes no account of a very important point in connection with 

 the ratio of the sexes, to which attention has not as yet been drawn. 



Among the type insects the sexes approach equality, but among the 

 melanics there are 110 (/</ to 73 $ $. This looks as if there is a 

 missing group of $ $ which correspond to the radiated cTcf, a fact 

 suggesting the operation of a lethal factor. It is curious, however, that 

 the missing $ $ should be restricted to the melanics, and it looks as if 

 the lethal factor is only effective when a female is both radiated and 

 melanic. If this were so, the ratio of the sexes would be much closer to 

 the figures actually obtained, but on the other hand the number of 

 radiated (/(/ should be only 26, instead of 43 as recorded. 



In trying to account for this unusual sex ratio, if only the factor for 

 radiation were in spite of the evidence found to be dominant, an analogy 



