MIMETIC S. AMERICAN BUTTERFLIES 273 



witnessing the common effect of local influences. But 

 this and every other explanation, except Natural Selection, 

 leave as a mere coincidence the fact that the first-named 

 three groups contribute the vast majority of the species, 

 and undoubtedly provide the models for the others. 

 Under Natural Selection the interpretation is easy ; the 

 groups in question are specially defended by unpalatable 

 qualities, and it is to tfieir advantage to warn their enemies 

 by a common advertisement. The Nymphaline, Erycinid, 

 and Pierine species may also be unpalatable and fall into 

 the same Mlillerian (Synaposematic) ^ combination, or 

 they may be edible and gain advantage by living on the 

 reputation of the three nauseous sub-families (Batesian 

 Mimicry or Pseudaposematic Resemblance). Taking all 

 available facts into consideration the former is the more 

 probable view. Not in Guiana alone, but wherever we 

 may travel in tropical America, groups of species of the 

 three Sub-Families tend to resemble each other and to 

 act as models for butterflies of other Families and Sub- 

 Families. In Venezuela, for example, they are reddish- 

 brown black-barred insects as in Guiana, but without the 

 tendency towards preponderant black in the hind-wings ; 

 in South Eastern Brazil they all possess an especially 

 light stripe, frequently bright yellow, along the hind- 

 wings, and a light spot, frequently white, at the apex of 

 the fore-wings ; at Ega, on the Upper Amazon, they all 

 gain a rich chestnut-brown ground colour ; still further 

 west, the brown ground colour is much less dark than at 

 Ega, and of a very characteristic shade. Why should 

 these three Sub-Families be so conspicuously subject to 

 the common influence of locality? Why should they more 

 than all other butterflies arrive independently at the same 

 evolutionary stage as regards visible characters ? Why 

 should Sexual Selection operate so exclusively upon them 

 in the direction of producing a common likeness ? None 

 of these questions can be answered. The facts remain 

 mere coincidences under all theories except Natural 

 Selection. In other words, Natural Selection is the only 

 satisfactory interpretation. 



^ Proc. Ent. Soc. Lond., 1897, p. xxix, n. 



POULTON T 



