The ESSEX FIELD CLUB. 257 



In ignorance of the optical effect producible by this arrangement of 

 colour he had in 1880 and since, in common with other naturalists, attempted 

 to explain the white colours of the undersides of birds, &c., as being of purely 

 physical origin. That explanation he now unreservedly withdrew in favour 

 of protection by concealment. 



With reference to the work on colour adaptability in individuals, as shown 

 by the illustrations of caterpillars, he thought that the lecturer had been too 

 modest in concealing his own share in this most important work. Although 

 he (the President) had by observation arrived at the conclusion that such 

 adaptability existed and had claimed natural selection as an efficient cause of 

 the phenomenon, it was only the experimental investigations of Prof. Poulton, 

 carried on with such consummate skill and patience, that had placed these 

 deductions on a solid basis of irrefutable facts. As an example of conceal- 

 ment b}' adventitious means he reminded them that they in Essex had the 

 well-known case of the larva of the Essex Emerald Moth (Geometra smamg- 

 dana; see Essex Naturalist, vol. I., p. 120). 



The President also expressed concurrence with the strictures which the 

 lecturer had imposed upon the conclusions drawn from the experiments of 

 those who, like Plateau, had actually tasted insects having warning colours 

 and because they could find no unpleasant taste had inferred that the whole 

 theory of distastefulness was erroneous. It was impossible to institute a 

 comparison between the senses of taste and smell of man and of insect-eating 

 birds and animals. Distastefulness might be associated with quite other 

 characters than those of taste or smell as interpreted by our senses. 

 Cantharidin, for example, a product of the blister-beetle, would be an 

 extremely unpleasant thing for a bird or animal to get into its mouth 

 although possessed of no distinctive smell as far as we know. An insect 

 producing this compound as an active defensive principle might derive the 

 full advantage of having warning colours without any nauseous smell or taste 

 at all. The danger would only be realised after the insect had been taken into 

 the mouth by its enemy. Hence the value in such cases of danger signals. 



The President went on to say that the development of the Miillerian 

 theory of mimicry in the hands of Prof. Poulton was a source of immense 

 gratihcation to him since he (the speaker) as the lecturer had told them, had 

 been very largely responsible for the adoption and promulgation of that 

 theory in its initial form in this country. It was the late Charles Darwin 

 who had first sent him in 1879 the publication, Kosmns, containing Fritz 

 Miiller's modest little paper, accompanied by one of his characteristic post- 

 cards asking him to see if there was anything in it. On looking through the 

 paper he came at once to the conclusion that there was a very great deal in it 

 — how much, they had perhaps been able to realize from the Hope Professor's 

 remarks that evening. Although he was himself a firm believer in the appli- 

 cation of Darwinian principles to the cases comprised under the general 

 term " Miillerian Mimicry," he thought it desirable to point out, by way of 

 answer to those who had from the beginning opposed the new ideas with the 

 charge of being too theoretical, that quite apart from the question of the 

 truth of the theory, its utility under the influence of Prof. Poulton had now 

 been demonstrated beyond cavil. Inspired by the new idea the lecturer had 

 set observers and collectors systematically at work in ^various parts of the 



