In addition to these three factors, there are, we believe, some others. Before proceeding to a consideration of these, it is important to study carefully the _modus operandi_ of natural selection, or, in other words, the nature of the struggle for existence, as many of the statements contained in recent books on evolution seem to us to be based upon a mistaken conception of this important factor. As usual, Darwin’s disciples have failed to improve upon the account he gave of the nature of the struggle for existence. This is set forth in Chapter III. of the _Origin of Species_. “The causes,” writes Darwin (new edition, p. 83), “which check the natural tendency of each species to increase in number are most obscure. Look at the most vigorous species; by as much as it swarms in numbers, by so much will it tend to increase still further. We know not exactly what the checks are even in a single instance.” This is perfectly true. Nevertheless elaborate theories of protective and warning colouration and mimicry have been built up on the tacit assumption that the checks to the multiplication of all, or nearly all, species are the creatures which prey upon them. Possibly no Wallaceian asserts this in so many words, but it is a logical deduction from the excessive prominence each one gives to the various theories of animal colouration; for, if the chief foes of an organism are not the creatures which prey upon it, how can the particular shade and pattern of its coat be of such paramount importance to it? Checks on Increase We shall endeavour to show that there are checks on the increase of a species far more potent than the devastation caused by those creatures which feed upon it. Let us, however, first briefly set forth some of the checks on the multiplication of organisms which Darwin mentions in the _Origin of Species_. “Eggs, or very young animals,” he says, “seem generally to suffer the most, but this is not invariably the case.” This is, as we have already insisted, a most important point to be borne in mind, especially when considering the various current theories of animal colouration. When once the average animal has become adult its chances of survival are enormously increased. A second check mentioned by Darwin is the limitation of food supply. “The amount of food for each species,” he writes (p. 84), “of course gives the extreme limit to which each can increase; but very frequently it is not the obtaining food, but the serving as prey to other animals, which determines the average numbers of a species. Thus there seems to be little doubt that the stock of partridges, grouse, and hares on any large estate depends chiefly on the destruction of vermin. . . . On the other hand, in some cases, as with the elephant and rhinoceros, none are destroyed by beasts of prey.”