My own view is that the regenerative capacity is not something primary, but rather an adaptation to the organism's susceptibility to injury, that is, a power which occurs in organisms in varying degrees, proportionate to the degree and frequency of their liability to injury. Regeneration prevents the injured animal from perishing, or from living on in a mutilated state, and in this lies an advantage for the maintenance of the species, which is the greater the more frequently injuries occur in the species, and the more they menace its life directly or indirectly. A certain degree of regenerative capacity is thus indispensable to all multicellular animals, even to the highest among them. We ourselves, for instance, could not escape the numerous dangers of infection by bacilli and other micro-organisms if our protective outer skin did not possess the faculty of regeneration, at least so far that it can close up a wound and fill up with cicatrice-tissue a place where a piece of skin has been excised. Obviously, then, the mechanism which evokes regeneration must have been preserved in some degree and in some parts at every stage of the phyletic development, and must have been strengthened or weakened according to the needs of the relevant organism, being concentrated in certain parts which were much exposed to injury and withdrawn from other rarely threatened parts. Thus the great diversity which we can now observe in the strength and localization of the regenerative capacity has been brought about. But all this can only be regarded as adaptation. I should like to submit a few examples to show that the regenerative capacity is by no means uniformly distributed, and that, as far as we can see, it is greater or less in correspondence with the needs of the animal, both in regard to the whole and to particular parts.