 As this whole volume is one long argument, it may be convenient to the reader to have the leading facts and inferences briefly recapitulated, that many engrave objections may be advanced against the theory of dissent with modification through natural selection. I do not deny. I have endeavored to give them their full force. Nothing at first can appear more difficult to believe than that the more complex organs and instincts should have been perfected not by means superior to, though analogous with, human reason, but by the accumulation of innumerable slight variations, each good for the individual possessor. Nevertheless, this difficulty, though appearing in our imagination and superbly great, cannot be considered real if we admit the following propositions, namely, that gradations in the perfection of any organ or instinct, which we may consider, either do now exist or could have existed, each good of its kind, that all organs and instincts are, in ever so slight a degree, variable, and lastly, that there is a struggle for existence leading to the preservation of each profitable deviation of structure or instinct. The truth of these propositions cannot, I think, be disputed. According to geographical distribution, the difficulties encountered on the theory of dissent with modification are grave enough. All the individuals of the same species, and all the species of the same genus, or even higher group, must have descended from common parents, and therefore in however distant and isolated parts of the world they are now found. They must, in the course of successive generations, have passed from one part to the others. We are often wholly unable even to conjecture how this could have been affected, yet as we have reason to believe that some species have retained the same specific form for very long periods, enormously long as measured by years, too much stress ought not to be laid on the occasional wide diffusion of the same species, for during very long periods of time there will always be a good chance for wide migration by many means. A broken or interrupted range may often be accounted for by the extinction of the species in the intermediate regions. It cannot be denied that we are as yet very ignorant of the full extent of the various climactic and geographical changes which have affected the earth during modern periods, and such changes will obviously have greatly facilitated migration. On this doctrine of the extermination of an infinitude of connecting links between the living and extinct inhabitants of the world, and at each successive period between the extinct and still older species, why is not every geological formation charged with such links? Why does not every collection of fossil remains afford plain evidence of the gradation and mutation of the forms of life? We meet with no such evidence, and this is the most obvious and forcible of the many objections which may be urged against my theory. Why again do whole groups of allied species appear, though certainly they often falsely appear, to have come in suddenly on the several geological stages? Why do we not find great piles of strata beneath the Celerian system stored with the remains of the progenitors of the Celerian group of fossils? For certainly on my theory such strata must somewhere have been deposited at these ancient and utterly unknown epics in the world's history. I can answer these questions and grave objections only on the supposition that the geological record is far more imperfect than most geologists believe. It cannot be objected that there has not been time sufficient for any amount of organic change, for the lapse of time has been so great as to be utterly inappreciable by the human intellect. The number of specimens in all our museums is absolutely as nothing compared with the countless generations of countless species which certainly have existed. We should not be able to recognize a species as the parent of any one or more species if we were to examine them ever so closely, unless we likewise possess many of the intermediate links between their past or parent and present states, and these many links we could hardly ever expect to discover owing to the imperfection of the geological record. Most existing doubtful forms could be named which are probably varieties, but who will pretend that in future ages so many fossil links will be discovered that naturalists will be able to decide on the common view whether or not these doubtful forms are varieties? As long as most of the links between any two species are unknown, if any one link or intermediate variety be discovered it will simply be classed as another and distinct species. Only a small portion of the world has been geologically explored, only organic beings of certain classes can be preserved in a fossil condition, at least in any great number. Widely ranging species vary most and varieties are often at first local, both causes rendering the discovery of intermediate links less likely. It is interesting to contemplate an entangled bank clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being growth with reproduction, inheritance which is almost implied by reproduction, variability from the indirect and direct action of the external conditions of life, and from use and disuse, a ratio of increase so high as to lead to a struggle for life, and as a consequence to natural selection, entailing divergence of character and the extinction of less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals directly follows. There is grandeur in this view of life, with its several powers having been originally breathed into a few forms or into one, and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning, endless forms most beautiful and most wonderful, have been, and are being, evolved. Thanks for watching.