Section D.— Dublin, 1908.] 



On Diaposematism, or the Interchange of Characters between Distasteful 

 Forms. By F. A. Dixey, M.A., M.D. 



When in the year 1879 Fritz Miiller put forward his theory of common warning 

 colours, or the assimilation of one distasteful form to another for the sake of 

 mutual protection against insectivorous enemies, he recognised the probability, or 

 even certainty, that the approach would not necessarily be one-sided, but might 

 be in the strict sense convergent, each form in some respects advancing to meet 

 the other. This suggestion, however, so far as F. Muller was concerned, remained 

 only in the theoretical stage; it was never developed by him, and although he 

 mentioned a few instances in support of his view, he did not attempt to trace the 

 supposed mutually mimetic process in any detail. There is, nevertheless, much 

 evidence that such reciprocal approach, or interchange of obvious characters, does 

 actually occur; and some cases of mimicry are here exhibited, the peculiar features 

 of which are difficult to explain on any other hypothesis. 



Thus the resemblance between Leuceronia pharis, Boisd., and the form of 

 Nychitona medusa, Cram., which inhabits the same districts of Central Africa, 

 appears to be due to mutual assimilation, the Leuceronia having borrowed its 

 peculiar outline and the attenuation of the dark apical patch from the Nychitona, 

 while the wings of the latter form owe their spotlessness and the comparative 

 opacity of their white pigment, in both of which respects they differ from the 

 forms nearest to them b) r affinity, to imitation of the Leuceronia. 



Similarly, the mimetic relation between Heliconius as represented by H.guaricus, 

 Reak., or H. haenschi, St. and Riff., and certain Pierines or ' white ' butterflies 

 such as Pereute leucodrosime, Koll., and Pieris locusta, Feld, may very possibly be 

 due to an interchange of certain features between them. 



Again, there is in the Island of Bali a certain Pierine butterfly, Ixias baliensis, 

 Fruhst., the female of which presents a general resemblance to another Pierine, 

 Huphina corva, Wallace, found in the same island. In view of the usual aspect of 

 the nearest allies of these two forms respectively, the conclusion suggests itself 

 that the Ixias has assimilated its forewing to that of the Huphina, and the 

 Huphina its hind wing to that of the Ixias. 



The females of certain Central and South American Papilios, or ' Swallowtails' 

 (as P. iphidamas, Fabr., P. nephalion, Godt , &c.) are in close mimetic relation 

 with both sexes of some common species of the Pierine genus Euterpe (e.g., 

 E. approximata, Butl., E. tereas, Godt., &c.) The suggestion is offered that 

 although in most respects the Papilio has plainly influenced the Pierine, it is yet 

 due to the influence of the latter that the females of the former have not adopted 

 more closely the aspect of their own males. 



For this phenomenon of mutual approach, or reciprocal influence, the term 

 Diaposematism has been proposed by Professor Poulton. The possibility of its 

 occurrence has been questioned on a priori grounds, but, it would appear, without 

 sufficient reason. 



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