142 Mr. G. A. K, Marshall on Dia^wsematism. 



capable of producing the profound colour modifications 

 which have been attributed to them. When an insect 

 having such qualities mimics a really unpalatable species, 

 it seems higlily probable that the mimicry will have been 

 due to the operation of Bates' factor and not that of 

 Muller. For we must remember that birds have probably 

 been the principal agents in producing these effects, and 

 Professor Poulton has himself arrived at the conclusion 

 that the discriminative tastes of birds are not as highly 

 developed as those of mammals (Rep. Brit. Ass. 1887, 

 p. 764). As he there says, this is what we should rather 

 expect owing to the relative difference in their intelligence ; 

 and it is not therefore likely that a slightly unpleasant 

 taste in a butterfly will have a mimetic importance in 

 relation to birds, when it apparently remains undetected 

 by so intelligent an animal as a baboon. 



In conclusion, I must express the sincere regret I feel 

 at having to insist so much upon the points in which I 

 differ from my old friends Professor Poulton and ]3r. Dixey, 

 to whom I am so deeply indebted, not only for their con- 

 tinued personal kindness and encouragement, but also for 

 the stimulating influence of their many valuable publi- 

 cations, with the general tenor of which I am entirely in 

 accord. For although I have thought it necessary to 

 point out what I consider to be definite limitations to 

 Fritz Mliller's principle, I have yet a firm belief an its 

 reality as an objective factor which has profoundly in- 

 fluenced a large number of insects in the tropics. But I 

 am likewise impressed with the equal importance of Bates' 

 principle. I have at least the consolation of finding that 

 my friend Mr. Roland Trimen is in close agreement with 

 the views here advocated, and I have to offer him my 

 grateful thanks for kindly checking the greater part of my 

 manuscript, and for the valuable comments he has made 

 thereon. 



I can only hope that this discussion may serve to stimu- 

 late other naturalists in the tropics to undertake those 

 experiments and observations which are so much needed 

 for the furtherance of this fascinating: line of research. 



