Thus, from the point of view that is here taken, an animal does not become degenerate because it becomes parasitic, but the environment being given, some forms have found their way there; in fact, we may almost say, have been forced there, for these degenerate forms can only exist under such conditions. In conclusion, this much at least can be claimed for the mutation theory; that it meets with no serious difficulty in connection with the phenomena of degeneration. It meets with no difficulty, because it makes no pretence to explain the origin of adaptations, but can account for the occurrence of degenerate forms, if it is admitted that these appear as mutations, or as definite variations. Let us, however, not close our eyes to the fact that there is still much to be explained in respect to the degeneration of animals and plants. It is far from my purpose to apply the mutation theory to all adaptations; in fact, it will not be difficult to show that there are many adaptations whose existence can have nothing directly to do with the mutation theory. Protective Coloration That many species of animals are protected by their resemblance to their environment no one will probably deny. That we are ignorant in all cases as to how far this protection is necessary for the maintenance of the species must be admitted. That some of the resemblances that have been pointed out have been given fictitious value, I believe very probable. Resemblance in color between the organism and its environment has given to the modern selectionist some of his most valuable arguments, but we should be on our guard against supposing that, because an animal may be protected by its color, the color has been acquired on this account. On the supposition that the animal has become adapted by degrees, and through selection, we meet with all the objections that have been urged, in general, against the theory of natural selection. But if we assume here also that mutations have occurred without relation to the environment, and, having once appeared, determined in some cases the distribution of the species, we have at least a simple hypothesis that appears to explain the facts. If it be claimed that the resemblance is, in some cases, too close for us to suppose that it has arisen independently of the environment, it may be pointed out that it has not been shown that such a close resemblance is at all necessary for the continued existence of the species, and hence the argument is likely to prove too much. For instance, the most remarkable case of resemblance is that of Kallima, but in the light of a recent statement by Dean it may be seriously asked whether there is absolute need of such a close resemblance to a leaf. Even if it be admitted that to a certain extent the butterfly is at times protected by its resemblance to a leaf, it is not improbable that it could exist almost equally well without such a close resemblance.