. . . If we endeavour to give any explanation of Müllerian mimicry, we are of course met by many objections. How did it arise? Is there enough ground to work upon? Are there any factors besides Natural Selection, and if so what are they? We cannot, of course, in the present state of our knowledge, give answers that will satisfy persistent objectors, but those who have at all studied the subject do not see any particular difficulty in recognising that in the keen struggle for existence Natural Selection and Variation may in time weed down two or more distasteful species until they resemble each other in minute particulars. Mimicry is a progressive and continuous process: it is playing a large part in the history of nature in the present, as it has done in the past and will continue to do in the future. In a letter which I received a short time ago from Dr. Alfred Russel Wallace, after saying that the toll of each insect exacted by insect-eaters is reduced exactly in proportion as more and more species so nearly resemble each other as to be apparently almost identical, he writes as follows:--"Hence if any simple pattern of warning colour is acquired by one protected species, there is a tendency for many other species, both protected and non-protected, to acquire similar colours and patterns (by variation and selection). Also protective markings may be acquired in the same way, and some very conspicuous markings, when the insect is in motion, become highly protective when it is at rest in its natural surroundings." The latter remark is very important: we are too apt to forget the necessity of taking environment into consideration.

     Dr. Wallace is further of opinion that the beginnings of such peculiar markings are often due to the need for recognition on "the first differentiation of species, and does not doubt but that this acts with beetles as it certainly does with higher animals": such may be the case, but it hardly seems probable.