Coloration of the Mouths and Eggs of Birds. 271 



as having brought about the resemblances, " the less perfect 

 degrees of resemblance being, generation after generation, 

 eliminated '"' by enemies that failed to be deceived. 



There was, however, one class of case that still puzzled 

 Bates. The mimicry of an unpalatable animal by a palatable 

 one was easily explained. But equally good resemblances 

 occurred where both ''model" and "mimic" were un- 

 palatable ! Some of these, he thought, must be the effect 

 of a similar environment acting on organisms related by 

 affinity and already alike. Others, he apparently felt, were 

 real cases of mimicry*, though, as both parties to the resem- 

 blance were unpalatable, he confessed himself unable to 

 suggest the additional advantage, possessed by tbe " model " 

 alone. It is in virtue of this that the members of the genus 

 Napeogenes, for example, had come to mimic abundant and 

 flourishing, and therefore presumably less persecuted, species 

 of the Ithomise. Evidently the idea of varying degrees of 

 unpleasantness failed to strike him (as it also failed to strike 

 Miiller); evidently, too, the advantage of sharing in the 

 notoriety of the more abundant form, to avoid the numerous 

 mistaken attacks that fall on a little-known species, did not 

 occur to him. 



Fritz Miiller, writing in ' Kosmos^ in May 1879, tried to 

 solve the difficulty. He suggested that young animals, in 

 sampling the qualities of unpalatable species, probably 

 destroy about an equal number of the members of each such 

 species with a separate colour-pattern, before learning to 

 leave them alone altogether. It would follow that a scarce 

 species, while losing the same absolute number of indi- 

 viduals from this cause, would lose a far higher percentage 

 than an abundant one, and might profitably, therefore, 

 mimic the latter. Again, it would be advantageous for two 

 equally unpleasant and abundant species to adopt the same 

 coloration, as, sharing the loss, each would now lose only 



* As I read him : Prof. Poulton, however, doubts whether, in spite 

 of his use of the word mimicry, Bates really regarded these cases as 

 such. 



