580 Mr. Louis B. Prout on Xanthorhoe ferrugata 



analogous to that of Mendel's classic " round " and 

 " angular " peas, or Raynor's Abraxas grossulariata and 

 ab. fiavofasciata (cfr. " Ent. Record," xv, pp. 142-144) ; no 

 case, that is to say, in which a crossing of the two colours 

 has resulted in the appearance of a first generation mani- 

 festing one colour only (Mendel's " Dominant.") This, I 

 apprehend, is not necessarily fatal to the application of 

 the Mendelian hypothesis, as it is always conceivable that 

 none of the pairings may have happened to be made with 

 sufficiently pure stock; assuming the black to be the 

 dominant colour, it is still not impossible that all those 

 which were mated with purple specimens chanced to be 

 really " hybrids" in their organization, and in this event a 

 part of the latent purple element in them should, in 

 fertilization, meet the purple element of the " recessive," 

 and result in specimens of that colour. But it seems to 

 me improbable that this should always have happened, 

 considering the number of pairings obtained ; it must be 

 remembered that hybrids only outnumber pure dominants 

 in the proportion of 2 : 1. 



Further, I do not see how to account for the reappear- 

 ance of black specimens in all my considerable broods of 

 purple X purple. If the recessive colour appears only in 

 pure recessive individuals, two of such, when mated, should 

 always breed true. And following the same line of thought, 

 one feels that the black pairings ought not to breed true 

 with the persistence which experience has revealed; for 

 two-thirds of them ought to be veritable "hybrids" with 

 simply an external dominant character. 



Taking all the facts into consideration, it thus appears 

 demonstrable that the colour dimorphism of Xanthorhoe 

 ferrugata does not obey Mendelian law. If there is any 

 correlation at all between the colouring and gametic 

 purity, it must be of so involved a nature as to baffle our 

 present powers of discernment. For instance, it is possible, 

 on certain analogies which might be adduced, that the 

 dominant form of this species may be a constantly black 

 or a constantly purple one, and the " recessive " a variable 

 one in colour, one of its forms being indistinguishable — ■ 

 so far as the human eye is yet trained — from the 

 "dominant." Or conversely, the recessive may be con- 

 stant to one colour and the dominant variable. To me, 

 however, the simplest view is still that which I deduced 

 from my work at the time when it was undertaken, and 



