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Show 1887.] VALUE OF COLOUR AND MARKINGS IN INSECTS. 2ZZ2/ advantage, that they only include insects which have been subjected to actual experiment. Although the tables comprise so few instances, I think that the resemblances of colour and pattern are most remarkable, and hard to explain under any other theory. My suggestion does at any rate point out a very obvious use for the resemblances. The advantages which every conspicuous and nauseous or dangerous species would gain by setting as simple a lesson as possible to tbe foes of its class, would be so great that there is no difficulty whatever in the supposition that every stage towards convergence in colours and in patterns would have been beneficial, and, as such, would have come under the influence of natural selection. It is to be noted that advantage would accrue in the greater thoroughness of the education, no less than by shortening the process; for a few colours, with a few simple patterns scattered over a number of species, would be remembered more easily than a larger number with a separate pattern in nearly every species. I am aware that this suggestion is but an extension to the whole group of conspicuous insects of the explanation offered by Fritz Muller to a fact which seemed for a long time an inexplicable difficult}', tbe undoubted fact that conspicuous butterflies presumably protected in the most complete manner by nauseous attributes, nevertheless mimic each other in the most unmistakable way. Bates, the original discoverer of " mimicry * in the animal kingdom, pointed out these apparently mysterious resemblances in the paper in which "mimicry" was itself "explained and illustrated. Wallace looked upon these obscure similarities between protected forms as due to some unknown cause connected with locality. It remained for Dr. Fritz Muller to explain the difficulties in a paper entitled " Ituna and Thyridia; a remarkable case of Mimicry in Butterflies " (' Kosmos,' May 1879, p. 100). Arguing from the instance of these two genera, which both belong to protected groups and which resemble each ether, Dr. Muller suggested that under these circumstances an advantage would be gained by each of them, because the number of species which must be sacrificed to the inexperience of young birds and other enemies would be made up by both of them instead of by each independently. This paper was translated by Prof. Meldola, and appeared in the 'Proc. Ent. Soc. Lond.' (1879, p. xx). In a subsequent paper by Dr. Muller (' Kosmos,' v. Jahrgang, 1881), the same subject is considered in greater detail, and the results are accepted and expounded by Wallace in 'Nature' (vol. xxvi. p. 86). The mathematical aspect of the subject was, however, inaccurately stated in this last paper, the correct statement being supplied by Mr. Blakiston and Mr. Alexander of Tokio, Japan; the correction being published in letters by Mr. Wallace and Prof. Meldola to 'Nature' (vol. xxvii. p. 481). Subsequently a letter appeared in ' Nature' (vol. xxix. p. 405) from Mr. Blakiston and Mr. Alexander, giving the complete mathematical statement of the advantages gained by each of the protected species. The law is given in these words, " Let there be two species of insects equally distasteful to young birds, and let it be supposed that the |
