But having now concluded this brief review of the leading arguments in favour of organic evolution, and having expressed as forcibly as I am able my own opinion upon them, I do not wish it to be supposed, either that I am intolerant of opinions which are held by others, or that I have been trying to, "make out a case" by suppressing adverse facts. I am not intolerant, because I believe that dissent from the general doctrine of evolution can only arise either from ignorance of some special departments of science, or from a bias of feeling against the doctrine--to both of which weaknesses evolutionists can afford to be indulgent. And in order to show that I have not been trying unfairly to make out a case, I shall conclude by briefly reviewing the arguments which have been adduced against the doctrine in question. The only argument of this kind that I know from the side of reason (if we neglect those special objections which have been fully shown by Mr. Darwin himself to be based on inadequate information or erroneous conception, and therefore futile), is that which says:--Evolution, if true, can only be proved so by an actual observation of the process, and as no one pretends to have witnessed the transmutation of species, it follows that evolution has not been proved. Now, it is perfectly right to draw a clear distinction between a theory and a demonstration; but it is a great mistake to suppose that a theory may then only be admitted by science when it has been demonstrated. Bishop Butler tells us that "Probability is the guide of life," and not less true is it that probability is likewise the guide of science. The business of science, as of common life, is to estimate correctly the relative degrees of probability presented by this and that theory or hypothesis; when once a theory or hypothesis is demonstrated it ceases to be a matter of scientific inquiry, and becomes a matter of scientific fact. Thus received, we have to consider the doctrine of evolution as certainly standing in the first rank of scientific theories in respect of probability sustained by evidence, although no less certainly not demonstrated as a matter of scientific fact. But when a theory has been raised to such a level of probability as this, it is, for all practical purposes, as good as a demonstration. Thus, in the particular instance before us, even if the sceptical demand for evidence, which from the nature of the case is clearly impossible, were granted, and if we could actually observe the transmutation of species, the fact would not exert any further influence on the progress of science than is now exerted by the large and converging bodies of evidence which leave no other rational theory open to us than that such transmutation has taken place. Therefore, it seems to me, the hypercritical objection which we are considering is really founded on a misconception of scientific method, and of what it is that justifies a scientific doctrine. Assuredly, in