It is chiefly among insects and especially among butterflies that we find the greatest number of such cases. Several of these have been minutely studied and every detail has been investigated so that it is difficult to understand how there can still be disbelief in regard to them. If the many and exact observations which have been carefully collected and critically discussed for instance by Poulton[47] were thoroughly studied the arguments which are still frequently urged against mimicry would be found untenable; we can hardly hope to find more convincing proof of the actuality of the processes of selection than these cases put into our hands. The preliminary postulates of the theory of mimicry have been disputed, for instance, that diurnal butterflies are persecuted and eaten by birds, but observations specially directed towards this point in India, Africa, America and Europe have placed it beyond all doubt. If it were necessary I could myself furnish an account of my own observations on this point. In the same way it has been established by experiment and observation in the field that in all the great regions of distribution there are butterflies which are rejected by birds and lizards, their chief enemies, on account of their unpleasant smell or taste. These butterflies are usually gaily and conspicuously coloured and thus--as Wallace first interpreted it--are furnished with an easily recognisable sign: a sign of unpalatableness or _warning colours_. If they were not thus recognisable easily and from a distance, they would frequently be pecked at by birds, and then rejected because of their unpleasant taste; but as it is, the insect-eaters recognise them at once as unpalatable booty and ignore them. Such _immune_[48] species, wherever they occur, are imitated by other palatable species, which thus acquire a certain degree of protection. It is true that this explanation of the bright, conspicuous colours is only a hypothesis, but its foundations--unpalatableness, and the liability of other butterflies to be eaten,--are certain, and its consequences--the existence of mimetic palatable forms--conform it in the most convincing manner. Of the many cases now known I select one, which is especially remarkable, and which has been thoroughly investigated, _Papilla dardanus_ (_merope_), a large, beautiful, diurnal butterfly which ranges from Abyssinia throughout the whole of Africa to the south coast of Cape Colony.