In birds, the legs and wings are not supposed to have the power to regenerate,[48] but in two forms[49] at least the beak has been found to possess remarkable powers of regeneration. There are a few very dubious observations in regard to the regeneration in man of superfluous digits that had been cut off.[50] These examples might be added to by others in the groups cited, and also by examples taken from the smaller groups of the animal kingdom, but those given will suffice, I think, to show that the power to regenerate is characteristic of entire groups rather than individual species. When exceptions occur, we do not find them to be forms that are obviously protected, but the lack of regeneration can rather be accounted for by some peculiarity in the structure of the animal. If this is borne in mind, as well as the fact that protected and unprotected parts of the same animal regenerate equally well, there is established, I think, a strong case in favor of the view that there is no necessary connection between regeneration and liability to injury. We may therefore leave this side of the question and turn our attention to another consideration. It will be granted without argument that the power of replacement of lost parts is of use to the animal that possesses it, especially if the animal is liable to injury. Cases of usefulness of this sort are generally spoken of as adaptations. The most remarkable fact in connection with these adaptive responses is that they take place, in some cases at least, in parts of the body where they can never, or at most very rarely, have taken place before, and the regeneration is as perfect as when parts liable to injury regenerate. Another important fact is that in some forms the regeneration is so slow that if the competition amongst the animals was very keen those with missing legs, or eyes, or tails, would certainly succumb; yet, if protected, they do not fail to regenerate. If, therefore, the animal can exist through the long interval that must elapse before the lost part regenerates, we cannot assume that the presence of the part is of vital importance to the animal, and hence its power to regenerate could scarcely be described as the result of a “battle for existence,” and without this principle “natural selection” is powerless to bring about its supposed result. It is extremely important to observe that some cases, at least, of regeneration are not adaptive. This is shown in the case where a new head regenerates at the posterior end of the old one in _Planaria lugubris_, or where a tail develops at the anterior end of a posterior piece of an earthworm, or when an antenna develops in place of an eye in several crustacea. If we admit that these results are due to some inner laws of the organism, and have nothing to do with the relation of the organism to its surroundings, may we not apply the same principle to other cases of regeneration in which the result is useful?