I still adhere entirely to this explanation; not of course in the sense that an actual physical struggle has ever taken place between the mortal and immortal varieties of any species. If Götte understood me thus, he may be justified by the brief explanations given in the essay to which I have alluded; but when he also attributes to me the opinion that such hypothetically immortal Metazoa had but a very limited period for reproduction, I fail to see what part of the essay in question can be brought forward in support of his statement. Only under some such supposition can I be reproached with having assumed the existence of a process of natural selection which could never be effective, because any advantage which accrued to the species from the shortening of the duration of life could not make itself felt in a more rapid propagation of the short-lived individuals. The statement ‘that in this and in every other case it is a sufficient explanation of the processes of natural selection to render it probable that any kind of advantage is gained’[81] is indeed erroneous. The explanation ought rather to be ‘that the forms in question would for ever transmit their characters to a greater number of descendants than the other forms.’ I have not however as yet attempted to think out in detail such processes of natural selection as would limit the somatic part of the Metazoan body to a short term of existence, and I only wished to emphasize the general principle lying at the basis of the whole process, without stating the precise manner in which it operates. If I now attempt to take this course, and to reconstruct theoretically the gradual appearance of natural death in the Metazoa, I must begin by again alluding to Götte’s criticisms in reference to the operation of natural selection.