"The gregarious habit of certain larvae supplies a possible solution of the problem, if we are willing to accept the view that the distasteful quality of the imago, which warning colours are so well adapted to advertise, is itself merely a by-product due to the persistence of nauseous substances acquired through the protection afforded to the larva. For, although with the adult insect the effect of increased distastefulness upon the actions of the predator will be merely to make that individual predator avoid all members of the persecuted species, and so, unless the individual attacked possibly survives, to confer no advantage upon its genotype, with gregarious larvae the effect will certainly be to give the increased protection especially to one particular group of larvae, probably brothers and sisters of the individual attacked. The selective potency of the avoidance of brothers will of course be only half as great as if the individual itself were protected ; against this is to be set the fact that it applies to the whole of a possibly numerous brood. There is thus no doubt of the real efficacy of this form of selection, though it may well be doubted if all cases of insect distastefulness can be explained by the same principle."