602 Mr. J. C. Moulton on some of the principal Mimetic 



models ; and therefore the case just quoted does not throw 

 any difficulty in the way of the explanation I have given ; 

 but It is a very extraordinary one." 



This passage is a good example of the difficulties in 

 which Bates was placed by the mimetic likeness between 

 specially protected groups. Bates' suggested interpreta- 

 tion seems to indicate that the colour resemblances between 

 the Heliconinss and Ithomiioise had obscured in his mind 

 the essential structural differences between these widely 

 separated sub-families. (See Poulton, " Essays on Evolu- 

 tion," 1908, p. 327.) 



In each of the four combinations hitherto considered, 

 the Ithomiinm, Heliconime, and NympliaUnx are all repre- 

 sented. Combination IV alone contains no Pierine or 

 Danaine member. On the other hand, it provides us with 

 an Acrma, two Satyrinx, a Fapilio, and a Castniid moth. 

 No species belonging to any of these groups enter the 

 three other associations. 



The possibility of a single warning pattern gradually 

 changing in the passage from one locality to another, e.g. 

 from the brilliant striped pattern of the Guatemala- 

 Nicaraguan type to the more sombre colour of the 

 Ecuador, Peru, and Bolivia type, becomes conceivable 

 when we find transitional stages. Thus we may imagine 

 that the North-Central American type is an ancestral 

 dominant warning pattern, and that on proceeding towards 

 the south-east, the conditions gradually began to favour 

 a darker hind-wing, as in the Guianas, and a yellow band 

 and apical fore-wing markings, as in Eastern Brazil. The 

 favourable conditions here referred to include above all 

 the infiuence of changes in the patterns of the most dominant 

 and central models in the combinations. Following these 

 great associations westward, the apparent differences be- 

 tween the Ega Combination (III) and those of the East 

 and North, is found to be consistent with an underlying 

 similarity. Thus we here recognise in the black band of 

 the hind-wing and ihe yellow apical markings of the fore, 

 the characters of the North-Central American Combina- 

 tion (I). I have already mentioned instances showing 

 possible transitional stages between the Ega type and the 

 still more westerly association in Ecuador, Peru, and 

 Bolivia. 



