Of course it must be understood that in thus applying the principle of correlated growth, to explain the origin of adaptive structures where it is impossible to explain such origin by natural selection having from the first acted directly upon these structures themselves, Darwinists do not suppose that in all--or even in most--cases of correlated growth the correlated structures are of use. On the contrary, it is well known that structures due to correlated growth are, as a rule, useless. Being only the by-products of adaptive changes going on elsewhere, in any given case the chances are against these correlated effects being themselves of any utilitarian significance; and, therefore, as a matter of fact, correlated growths appear to be usually meaningless from the point of view of adaptation. Still, on the doctrine of chances, it is to be expected that sometimes a change of structure which has thus been indirectly produced by correlation of growth might happen to prove useful for some purpose or another; and in as many cases as such indirectly produced structures do prove useful, they will straightway begin to be improved by the direct action of natural selection. In all such cases, therefore, we should have an explanation of the _origin_ of such a structure, which is the only point that we are now considering. I think, then, that all this effectually disposes of the doctrine of "prophetic germs." But, before leaving the subject, I should like to make one further statement of greater generality than any which I have hitherto advanced. This statement is, that we must remember how large a stock of meaningless structures are always being produced in the course of specific transmutations, not only by correlation of growth, which we have just been considering, but also by the direct action of external conditions, together with the constant play of all the many and complex forces internal to organisms themselves. In other words, important as the principle of correlation undoubtedly is, we must remember that even this is very far from being the only principle which is concerned in the origination of structures that may or may not chance to be useful. Therefore, it is not only natural selection when operating indirectly through the correlation of growth that is competent to produce new structures without reference to utility. In all the complex action and reaction of internal and external forces, new variations are perpetually arising without any reference to utility, either present or future. Among all this multitude of promiscuous variations, the chances must be that some percentage will prove of some service, either from the first moment of their appearance, or else after they have undergone some amount of development. Such development prior to utility may be due, either to correlation of growth, to the structure having previously performed some other function, as already explained, or else to a