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Show 230 MIJ. E. B. POULTON ON THE PROTECTIVE [Mar. 1, species known to be nauseous or dangerous. There must certainly be a tendency towards a further general convergence, but the existing condition of convergence round a few well-marked types of pattern and colouring must be highly beneficial, and there was in this case no initial uniformity due to close affinity, upon which to base a general and uniform system. It was in fact a priori far more likely that the convergence of remote species should have been round a i'ew successful types, while the prevention of divergence among closely related species must ipso facto have tended to produce concentration round a single type. It will be shown below that Fritz Miiller's principle is probably attended by others, which also assist in producing convergence, at any rate in some cases. Another result of the different origin of the two classes of resemblance alluded to above is that the uniform warning colours of a large group of closely related species are less conspicuous, and in themsehes possess less of "warning" characteristics, than those of the smaller groups into which the isolated nauseous species tend to converge ; for the former depend largely upon some ornamental type of colour and marking, due to sexual selection, and prevalent before the time when the nauseous attributes arose. Such a tvpe has no doubt been modified in the direction of greater conspicuousness on the uppersides of the wings, while bright colours have appeared on their undersides, and the mode of flight has been changed into one which gives the colours their maximum effect; but still, in spite of these changes, the whole appearance of such large groups presents us with the ancestral sexually selected colours and patterns, which are of great beauty, and are no doubt still of great significance as secondary sexual characters. The success of such a stereotyped ornamental appearance for warning purposes has depended upon the modifications alluded to above, but principally upon the verv fact of* its prevalence and uniformity. On the other hand the smaller convergent groups of nauseous insects often present us with ideally perfect types of warning patterns and colours-simple, crude, strongly contrasted-everything subordinated to the paramount necessity of becoming conspicuous. For the nauseous attributes arising independently among the scattered species of many genera, or in all the species of small genera, instead of being chiefly concentrated among the members of some one or two dominant groups, it must have become impossible to rely upon the slightly altered ornamental appearance existing at the time when the attributes arose ; but it was necessary to appeal strongly to tbe memory of enemies by the acquisition of some special form of pattern and colour, in which everything is subordinated to the li warning" characteristics. In the one class the pre-existing ornamental appearance was sufficiently well known to serve as a warning; in the other class it was not sufficiently well known. It is quite clear that the two classes of resemblance which have been just considered must be carefully distinguished from true mimicry, in which the mimicking species is without anv unpleasant attribute, but shelters itself under the reputation of the (nearly |