In the next volume a great deal more will have to be said upon these matters--especially with regard to the causes other than natural selection which in my opinion are capable of explaining these so-called "difficulties." In the present connexion, however, all I have attempted to show is, that, whatever may be thought touching the supplementary theories whereby I shall endeavour to explain the facts of inutility, cross-sterility, and non-occurrence of free intercrossing, no one of these facts is entitled to rank as an objection against the theory of natural selection, unless we understand this theory to claim an exclusive prerogative in the field of organic evolution. This, as we have previously seen, is what Mr. Wallace does claim for it; while on the other hand, Mr. Darwin expressly--and even vehemently--repudiates the claim: from which it follows that all the three main objections against the theory of natural selection are objections which vitally affect the theory only as it has been stated and upheld by Wallace. As the theory has been stated and upheld by Darwin, all these objections are irrelevant. This is a fact which I had not myself perceived at the time when I mentioned these objections in a paper entitled _Physiological Selection_, which was published in 1886. The discussions to which that paper gave rise, however, led me to consider these matters more closely; and further study of Darwin's writings, with these matters specially in view, has led me to see that none of the objections in question are relevant to his theory, as distinguished from that of Mr. Wallace. This, I acknowledge, I ought to have perceived before I published the paper just alluded to; but in those days I had had no occasion to follow out the differences between Darwin and Wallace to all their consequences, and therefore adopted the prevalent view that their theories of evolution were virtually identical. Now, however, I have endeavoured to make it clear that the points wherein they differ involve the important consequences above set forth. All these the most formidable objections against the theory of natural selection arise simply and solely from what I conceive to be the erroneous manner in which the theory has been presented by Darwin's distinguished colleague. * * * * *