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Show 216 MR. E. B. POULTON ON THE PROTECTIVE [Mar. 1, Darwin's which enables us to point towards the purely sexual value of one factor in the appearance of certain butterflies; and by the same kind of observation it is likely that increasing stability will be given to tbe whole theory of sexual selection. Darwin noticed that the magnificent surface-colours which exist on many tropical butterflies, and which change with the position from which the insect is observed (being probably due to diffraction), become most brilliant when they are seen from the front, and at an angle which corresponds with that at which they would be seen by the female as the male butterfly approaches her. As a further test of the " warning " value of certain colours, we can use as a comparison the colours and patterns of certain larvse which are known to be "warning" only, or which at any rate cannot be sexual. After giving the list and the experimental details, I shall attempt to show that there are certain combinations of colour, and sometimes even certain patterns, which are generally distinctive of "warning" as apart from sexual coloration. And such differences of type are to be expected ; for the two systems of coloration appeal to a different class of animals and appeal to a different sense. The " warning " colours of insects appeal to a Vertebrate's sense of what is conspicuous; the sexual colours appeal to an Invertebrate's sense of what is beautiful. And it is one of the most remarkable facts in the study of comparative psychology that our own sense of what is beautiful entirely coincides with that of an insect, so that the difference in the two types of coloration depends entirely upon the sense alluded to above, and has probably no reference to the class of animals in which the sense exists. For, if we had no knowledge of tbe use and meaning of the colours of insects, we should all agree in maintaining that certain colours and patterns (which we now trace to the action of sexual selection) comprise all that is beautiful in the appearance of this class of animals, and we should draw a sharp line between these and other combinations of colour which we now recognize as possessing an entirely different significance. In the following instances it is unnecessary to enter upon any preliminary account, as the table contains all the details which I can find recorded. Of course this list must contain any cases (if tested) in which a conspicuous appearance is believed to be due to " mimetic" resemblance to another species protected by possessing some unpleasant attribute. I much regret that hardly any of these most interesting cases have been used for experiment (see Table IV., pp. 218-223). Looking at this fourth table, we find that the theory of warning colours is again confirmed in the most marked manner. Unfortunately the extremely interesting " mimetic" cases still lack the necessary experimental demonstration; although the intimidating larvse of C. elpenor and G. vinula are really mimetic of vertebrate appearances, and the former has been shown to be attended by a considerable amount of success. The only "mimetic" form in this last list is Sesia fuciformis, and in this case the mimicry is |
