Bates, however, besides making an ingenious application of the above principle to a special case, gave a real reason for something which was not at all obvious, viz. why one butterfly should be a gainer by closely resembling another; and this no one had hitherto been able to do. His surmise, which has since in many instances been confirmed, is as follows. Having first pointed out that the _Heliconea_ butterflies are a numerous, flourishing race, whilst those species that imitate them are poor in numbers, he says, “What advantages the _Heliconidæ_ possess to make them so flourishing a group, and, consequently, the object of so much mimetic resemblance, it is not easy to discover. There is nothing apparent in their structure or habits which could render them safe from persecution by the numerous insectivorous animals which are constantly on the watch in the same parts of the forest which they inhabit. It is probable they are unpalatable to insect enemies. Some of them have glands near the end of the abdomen which they protrude when roughly handled; it is well known that similar organs in other families secrete fetid liquids or gases and that these serve as a protection to the species. They have all a peculiar smell. I never saw the flocks of slow-flying _Heliconidæ_ in the woods persecuted by birds or dragon-flies, to which they would have been easy prey; nor when at rest on leaves did they appear to be molested by lizards, or the predaceous flies which were very often seen pouncing on butterflies of other families. If they owe their flourishing existence to this cause it would be intelligible why species whose scanty number of individuals reveals a less protected condition, should be disguised in their dress, and thus share their immunity. Is it not probable, seeing the excessive abundance of the one species and the fewness of individuals of the other, that the _Heliconea_ is free from the persecution to which the _Leptalis_ is subjected?”[107]