228 MR. E. B. POULTON ON THE PROTECTIVE [Mar. 1, 



birds would destroy the same number of individuals of each, before 

 they were educated to avoid them. Then if these insects are 

 thoroughly mixed, and become undistinguishable to the birds, a 

 proportionate advantage accrues to each over its former state of 

 existence. These proportionate advantages are inversely in the 

 duplicate ratio of their respective original numbers, compounded with 

 the ratio of the respective percentages that would have survived 

 without the mimicry." 



It had been previously argued that in the case of two protected 

 species which had thus come to resemble each other, the proportionate 

 advantage was cliiefly on the side of the one which was smaller in 

 numbers, and that when the numerical difference was great the 

 advantage to the other could be neglected. The amended law wliich 

 is quoted above shows, however, that the proportionate advantage is 

 always the same, and this is also enforced in another part of the same 

 letter: — " It must be remembered, however, that B does no harm to 

 A by mimicking it ; on the contrary the act of mimicry is of advantage 

 to A over its former state of existence as well as to B ; but A being 

 more numerous the advantage is less. Siill, after the assimilation, 

 neither has an advantage over the other. Proportionally they suffer 

 from tbe ravages of birds equally ; the percentage of losses is the 

 same ; they are on equal terms. No matter how long they continue 

 the association, neitber gains or loses on the other ; though through 

 one being more numerous it loses more individuals, yet equally in 

 proportion with the other. So that if one is twice as numerous as 

 the other at the time of assimilation, it must always — other condi- 

 tions being equal — remain twice as numerous." 



Dr. INIiiller's interpretation was at first criticized in man\' quarters, 

 the chief objection brought forward being the belief that birds do not 

 learn the meaning of the conspicuous colours by experience, but that 

 they avoid such insects by instinct, the ancestral experience having 

 become hereditary. There is, however, no direct evidence for this 

 view, and I think the account of J. Jenner Weir's observations upon 

 Lizards, and my own upon Lizards and Frogs (given in the two 

 Appendices to this paper), will go far to furnish an experimental 

 refutation of such a theory, so far as these animals are concerned. 

 In addition to this, I am assured by a very keen observer. Rev. G. J. 

 Burch, that recently hatched chickens certainly do peck at insects 

 which they afterwards learn to avoid without trial, and he believes 

 that the hen assists in their education by indicating that certain 

 insects are not fit for food. His observations were chiefly made upon 

 a common phytophagous Hymenopterous larva which is found upon 

 gooseberry (doubtless Netnatus ribesii). Another observation made 

 by Mr. Burch bears upon the same question. He offered his chickens 

 a quantity of chickweed, knowing that this plant was often given as 

 food to Linnets. The chickens ate the plant readily enough, but they 

 were all extremely unwell in consequence, and vomited freely. After 

 this Mr. Burch again offered them chickweed, but they had profited 

 by the experience and would not touch it. 



The chief attack upon Dr. Miiller's suggestion was made by Mr.W. 



