OCR Text |
Show 1887.] VALUE OF COLOUR AND MARKINGS IN INSECTS. 229 L. Distant (' Nature,' vol. xxvi. p. 105 ; and ' Rhopalocera Malayana,' pt. ii. p. 33) ; but all his objections were very completely answered by Prof. Meldola (' Ann. & Mag. Nat. Hist.' Dec. 1882), who, in his concluding sentences, largely anticipates that further extension of Fritz Midler's theory which is here brought forward, the suggestion that all the conspicuous and dangerous or distasteful species in any country will be found to share between them a few strongly contrasted colours, arranged in few and simple patterns again and again repeated. He says:-" I am persuaded that the extension of the theory of mimicry proposed by Fritz Muller marks a great advance in our views on this subject, which is so interesting as having been the first to which the Darwinian Theory of Evolution was applied with such success by Mr. Bates. Not only are we now in possession of a consistent theory which enables us to dispense witb mysterious and 'unknown local causes,' but other groups of facts hitherto incomprehensible are capable of explanation. Thus the prevalence of one type of marking and colouring throughout immense numbers of species in protected groups, such as the tawny species of Danais, the barred Heliconias, the blue-black Euplceas, and the fulvous A^rceas, is perfectly intelligible in the light of the new hypothesis. While the unknown factors of species-transformation have in these cases caused divergence in certain characters, other characters, viz. superficial colouring and marking, have been approximated or prevented from diverging by the action of natural selection, every facility having been afforded for the action of this agency by virtue of the near blood-relationship of the species concerned. When discussing the origin of mimicry, Mr. Darwin long ago suggested that it might have commenced at a time when the species were nearly related in marking and colouring." The suggestion here brought forward and depending upon the results which aie tabulated below, is a further extension of the same principles, so that certain resemblances between insects belonging to very different groups are accounted for on the supposition that natural selection has not only prevented divergence in nearly related forms which were originally similar, but has in other cases actually determined the convergence of widely separated forms which were originally unlike. This latter explanation of the resemblances was intended by Fritz Muller in his paper on " Ituna and Thyridia," for he looked upon these genera as widely separated, and their similarity as due to convergence. There appears, however, to be some dispute as to their true affinities. It is obvious that under Prof. Meldola's suggestion we shall expect to find a far greater similarity between the species of a large group of closely allied nauseous insects in any country than between those of other large groups protected in 'other ways; while, on the other hand, there is no necessity for the expectation of equal uniformity among the isolated nauseous species or even among those belonging to small museous groups. W e should rather expect the constant appearance of a few simple but very different patterns, made up of a few strongly contrasted colours ; and this is precisely the arrangement which is proved to obtain by the tabulation of the appearances of all such |