in numbers? In itself, certainly not; the red mimetic females could increase in number without causing any decrease of the yellow ones, for the red are in no way in conflict with the yellow, and we must not think of the number of individuals as so fixed for each species that it cannot increase. On the contrary, it _must_ increase, as soon as the conditions of existence are permanently improved, and this happens, in this case, through the mimetic protection of the red female. We can thus easily understand how mimetic and non-mimetic females can live side by side in Abyssinia. In all the rest of Africa, however, there are only mimetic females of _Papilio merope_, and none of the colour of the male; these last, therefore, have been crowded out by the mimetic form, not actively, but through the more frequent survival of the mimetic form, so that those like the male became gradually rarer, and finally died out--that is, ceased to occur. The matter is not so simple as it seems, and we shall best understand it by thinking of the dimorphism of the caterpillars of our hawk-moths, which we discussed before, in which the green form in the full-grown caterpillar is less well protected than the brown. In many species the brown form has crowded out the green, in others brown and green occur side by side, but the green is less abundant, and in some species very rare. This must be regarded as the simple result of the circumstance that a higher percentage of the green than of the brown caterpillars fall victims to enemies, and thus, in the course of generations, the green form becomes slowly but steadily rarer. This will be the case even if the newer and better adaptation raises the number of individuals (the 'normal number') in the species, for this increase must always be a limited one, even if it be very great, which is hardly likely in this case. For the normal number is not determined by the mortality at one stage, but by that at all the stages of life taken together. Thus a normal number always persists, notwithstanding the improved conditions for the species, and, on this assumption, the form under less favourable conditions cannot permanently hold its own with that under better conditions, but must gradually disappear. We can understand, then, that the primitive form of the _Papilio merope_ female may persist even for a long time side by side with the mimetic form in certain habitats. It is, probably, not a mere chance, that this should have happened just in Abyssinia, for, in that region, the mimetic female is still tailed--that is, she has not yet reached the highest degree of resemblance to her immune model. In the whole of the rest of Africa the process of the transformation of the female has already reached its highest point, and on the east and west coasts, as well as in South Africa, the primitive form of the species is now represented only by the male.