106 Mr. G. A. K. Marshall on Diaposcmatism, with reference 



I. The Association of Pereute and Heliconius. 



This case is of special interest because, with the next 

 one, it furnished the original basis for the theory we are 

 considering. It was dealt with by Dr. Dixey in Trans. 

 Ent. Soc. 1894, p. 29G, and further discussed in the Trans, 

 for 1896 (p. 72). The facts are briefly these : Certain 

 forms of the Pierine genus Pereute in Tropical America 

 exhibit an undoubted mimetic approach towards the 

 common Heliconius mclpomenc and its allies, whose upper- 

 side colouring is plain brown, with a broad red band across 

 the fore-wings. Now many species of Pereute have on the 

 under-side some distinct red spots at the base of the hind- 

 wing. Somewhat similar markings also occur in the 

 Hclicunii, but Dr. Dixey, quite justifiably, refuses the 

 explanation that these spots have been acquired by the 

 Pereute as part of their mimetic resemblance to Heliconius. 

 For he shows that not only can we find similar markings 

 in other American Pierines which have no mimetic 

 relationship with Heliconius or any of the red-spotted 

 Papilios, but further they are shown to occur independently 

 in Pierine genera in other parts of the world ; notably in 

 some species of the distasteful Eastern genus Delias, to 

 which he considers Pereute to be nearly allied. On these 

 grounds the spots are claimed as being Pierine in character. 

 How then are we to explain their presence in Heliconius ? 

 Any argument for parallel development is rejected by Dr. 

 Dixey, for he says : " If we assert them to be purely 

 ' accidental,' we are met by the fact that although they 

 are found in some species of both Papilio and Heliconius 

 that are apparently not the subject of mimicry, yet they 

 are most distinct and most prevalent in those species 

 which are copied by Pierine imitators" (I.e. 1894, p. 296). 

 Hence it is contended that the only satisfactory explana- 

 tion is that, in this particular respect, the Heliconii have 

 been influenced by, and approached, the Pereute, and that 

 therefore the red spots constitute a reciprocal or diapose- 

 matic character. 



Now, in order that any case of this kind may really 

 carry conviction as a proof of diaposematism it is necessary 

 to show that the reciprocal character which the model 

 is claimed to have acquired from the mimic must be one 

 that is abnormal in the genus of the model and its allies. 

 For if the character occurs frequently and independently 



