So firm a hold has the Darwinian doctrine of utility over the thoughts of those who have been trained in this school, that whenever it can be shown that a structure or a function is useful to an animal, it is without further question set down as the result of the death struggle for existence. A number of writers, being satisfied that the process of regeneration is useful to the animal, have forthwith supposed that, _therefore_, it must have been acquired by natural selection. Weismann has been cited as an example, but he is by no means alone in maintaining this attitude. It would be entirely out of place to enter here into a discussion of the Darwinian theory, but it may be well worth while to consider it in connection with the problem of regeneration. We might consider the problem in each species that we find capable of regenerating; or, if we find this too narrow a field for our imagination, we might consider the process of regeneration to have been “acquired by selection in the lower and simpler forms,” and trace its subsequent progress as it decreased in the course of phylogeny “in correspondence with the increase in complexity of organization,” or with the decrease of exposure to injury. At the risk of adopting the narrower point of view I shall confine the discussion to the possibility of regeneration being acquired, or even augmented, through a process of natural selection in any particular species. The opportunity to regenerate can only occur if a part is removed by accident or otherwise. On the Darwinian theory we must suppose that of all the individuals of each generation that are injured, _in exactly the same part of the body_, only those have survived or have left more offspring that have regenerated. In order that selection may take place, it must be supposed that amongst these individuals injured _in exactly the same region_, regeneration has been better in some forms than in others, and that this difference is, or may be, decisive in the competition of the forms with each other. The theory does not inquire into the origin of this difference between individuals, but rests on the assumption of individual differences in the power to regenerate, and assumes that these differences can be heaped up by the survival and inbreeding of the successful individuals; _i.e._ it is assumed that, by this picking out or selection through competition in each generation of the individuals that regenerate best, the process will become more and more perfectly carried out in the descendants, until at last each part has _acquired_ the power of complete regeneration.