on Mullerian Mimicry and Diaposematism. 565 



adequate account of the Miillerian conception. He has 

 no warrant, so far as 1 am aware, for the statement that 

 " in practice, the appUcation of the Mullerian interpretation 

 involves the assumption of a uniform standard of inedi- 

 bihty " ; a statement which amounts to saying that any 

 disparity of loss suffered by the less distasteful form 

 involves the exclusion of the Mullerian factor from any 

 assimilation it may acquire to the more distasteful. We 

 can imagine that the frontier-line separating the operation 

 of the two principles, though distinct, is fluctuating ; but 

 this does not justify any one in claiming the whole territory, 

 up to the point of absolute equality of distastel'ulness, as 

 an exclusive sphere of influence for the Batesian factor. 

 In this and in other respects, Mr. Marshall's criticism, so 

 far as it is effective, is directed not against the Miillerian 

 theory itself, but against an imaginary position which has 

 been erroneously endowed with the Miillerian name. 



There is a further factor which has an equally disturbing 

 effect with relative distastefulness on these numerical 

 calculations. It is that of relative conspicuousness. A 

 species poorly off in point of numbers may well suffer less 

 than a more abundant form by dint of possessing a pattern 

 which is more striking and so more easily remembered. 

 A further complication is afforded by the varying habits of 

 different species. It is by no means the case that all 

 distasteful butterflies take every means of advertising 

 themselves. There are differences between them in this 

 as in other respects. As Mr. Marshall has mentioned the 

 Erycinidse* in this connection (p. 133), I commend to his 

 notice the instructive case of Hades nodula, Westw., an 

 abundant insect which there is every reason to suppose 

 has acted as a model, but which nevertheless settles 

 habitually on the under side of leaves.f If, as is quite 

 possible, frequency of repetition is a factor in the rapidity 

 Avith which insectivorous animals learn their lesson (a 

 suggestion first made to me in a private letter by Mr. W. 

 F. H. Blandford), a distasteful insect with habits of 

 concealment might be more strongly influenced in the 

 Miillerian direction than a species with great powers of 

 advertisement though inferior in numbers. So far as 



* Mr. Wallace's paper appeared in the Trans. Ent. Soc. Lond. for 

 1863 ; not 1863, as stated by Mr. Marshall. 



t See Godman and Salvin ; Biol. Centr. Amer., Rhopal., I, 

 p. 374. 



