162 SCIENCE PROGRESS 



— which the author has analysed and for which he has invented an elaborate and 

 precise terminology. It is not too much to say that the marvels of " mimicry" in 

 the wide sense were never more vividly expounded, and that the essays afford a 

 valuable body of evidence in support of the theory of natural selection. Prof. 

 Poulton considers other interpretations of mimetic phenomena, that they are due 

 to environmental influences, that they are in part due to the operation of sexual 

 selection, and that they are due to " internal developmental causes, compelling 

 different species to pass through similar phases." We are not sure that he does 

 justice to this last view, "the theory of internal causes" — the bathmist position, 

 but that is probably because it has never been clearly stated by any of its advocates. 

 In any case the author contrasts this and other rival interpretations with the 

 selectionist interpretation, and one cannot help sharing his satisfaction with his 

 master-key. Some of the cases to which he applies the selectionist interpretation 

 are extraordinarily intricate and subtle, but these cannot be briefly cited. We read 

 of the Sudanese Locustid Myrmecophana, on whose body the slender-waisted form 

 of an ant is represented in black pigment, the rest of the body being inconspicuous 

 against an appropriate background ; of a Central American Membracid which has 

 an enormous prothoracic shield shaped like an ant, and concealing the rest of the 

 body ; of insects that lose their shadows, like students of the Black Art ; of a South 

 American moth like a leaf attacked by a fungus which has " skeletonised " certain 

 parts and is still at work upon others ; but these are relatively simple cases com- 

 pared with some of the best instances of Miillerian resemblance. In true or 

 Batesian mimicry the mimetic animal resembles an object which positively repels 

 its enemies or positively attracts its prey, as when a harmless snake resembles 

 a poisonous one ; in Miillerian mimicry a similar kind of warning coloration is 

 shared by a number of unrelated species. " Each species which falls into a group 

 with common warning or synaposematic colours contributes to diminish the 

 destruction of the other members." It is interesting to notice that the researches 

 on mimicry pursued during the last twenty years, in which Poulton has been one 

 of the foremost workers, tend to increase the number of illustrations of Miillerian 

 mimicry and to reduce the number of Batesian cases. 



Though most of the contents of this volume have been published before, the indi- 

 vidual essays have been revised, and it is very convenient to have them brought 

 together and thoroughly indexed. They are prefaced by an introduction, written with 

 considerable heat, in which the author protests against the style of recent writings 

 by enthusiastic investigators of Mutation and Mendelism. The writings in question 

 are injurious, according to Poulton, because of their dogmatism, their assumptions, 

 their appropriation under the name of Mendel of results which the present genera- 

 tion owes to Weismann, their exaggeration of the value of certain kinds of results 

 and methods, and their contemptuous depreciation of other lines of investigation 

 which have proved themselves valid. Probably Prof. Poulton does well to be 

 angry, and it is a relief from the monotony of the all-round toleration which 

 enervates the philosophic temperament. It is certain, however, that Bateson and 

 Poulton are working at different corners of the same great problem, that their 

 inquiries are complementary, not antithetic, and that their respective researches 

 in the breeding-pen and in the meadow, in the under-world of the gametes and in 

 the open-air struggle for existence, are being conducted in the scientific mood 

 characteristic of Darwin who inspired them both, who turned unembarrassed from 

 genetic to cecological inquiry and back again, as the needs of the problem 

 demanded. 



J. A. Thomson. 



