following the truest method of inductive research in allowing any amount of latitude to his speculative thought in the direction of scientific theorizing. For it follows from the above distinctions that the danger of speculation does not reside in the width of its range, or even in the impetuosity of its vehemence. Indeed, the wider its reach, and the greater its energy, the better will it be for the interests of science. The only danger of speculation consists in its momentum being apt to carry away the mind from the more laborious work of adequate verification; and therefore a true scientific judgment consists in giving a free rein to speculation on the one hand, while holding ready the break of verification with the other. Now, it is just because Darwin did both these things with so admirable a judgment, that he gave the world of natural history so good a lesson as to the most effectual way of driving the chariot of science.

This lesson we have now all more or less learnt to profit by. Yet no other naturalist has proved himself so proficient in holding the balance true. For the most part, indeed, they have now all ceased to confound the process of speculation per se with the danger of inadequate verification; and therefore the old ideal of natural history as concerned merely with collecting species, classifying affinities, and, in general, tabulating Facts, has been well-nigh universally superseded. But this great gain has been attended by some measure of loss. For while not a few naturalists have since erred on the side of insufficiently distinguishing between fully verified principles of evolution and merely speculative deductions therefrom, a still larger number have formed for themselves a darwinian creed, and regard any further theorizing on the subject of evolution as ipso facto unorthodox.

Having occupied the best years of my life in closely studying the literature of Darwinism, I shall endeavour throughout the following pages to avoid both these extremes. No one in this generation is able to imitate Darwin, either as an observer or a generalizer. But this does not hinder that we should all so far endeavour to follow his method, as always to draw a clear distinction, not merely between observation and deduction, but also between degrees of verification. At all events, my own aim will everywhere be to avoid dogmatism on the one hand, and undue timidity as regards general reasoning on the other. For everything that is said justification will be given; and, as far as prolonged deliberation has enabled me to do so, the exact value of such justification will be rendered by a statement of at least the main grounds on which it rests. The somewhat extensive range of the present treatise, however, will not admit of my rendering more than a small percentage of the facts which in each case go to corroborate the conclusion. But although a great deal must thus be necessarily lost on the one side, I am disposed to think that more will be gained on the other, by presenting, in a terser form than would otherwise be possible, the whole theory of organic evolution as I believe that it will eventually stand. My endeavour, therefore, will be to exhibit the general structure of this theory in what I take to be its strictly logical form, rather than to encumber any of its parts by a lengthy citation of facts. Following this method, I shall in each case give only what I consider the main facts for and against the positions which have to be argued; and in most cases I shall arrange the facts in two divisions, namely, first those of largest generality, and next a few of the most special character that can be found.

As explained in the Preface, the present instalment of the treatise is concerned with the theory of evolution, from the appearance of the Origin of Species in 1859, to the death of its author in 1882; while the second part will be devoted to the sundry post-Darwinian questions which have arisen in the subsequent decade. To the possible criticism that a disproportionate amount of space will thus be allotted to a consideration of these post-Darwinian questions, I may furnish in advance the following reply.

In the first place, besides the works of Darwin himself, there are a number of others which have already and very admirably expounded the evidences, both of organic evolution as a fact, and of natural selection as a cause. Therefore, in the present treatise it seemed needless to go beyond the ground which was covered by my original lectures, namely, a condensed and connected, while at the same time a critical statement of the main evidences, and the main objections, which have thus far been published with reference to the distinctively Darwinian theory. Indeed while re-casting this portion of my lectures for the present publication, I have felt that criticism might be more justly urged from the side of impatience at a reiteration of facts and arguments already so well known. But while endeavouring, as much as possible, to avoid overlapping the previous expositions, I have not carried this attempt to the extent of damaging my own, by omitting any of the more important heads of evidence; and I have sought to invest the latter with some measure of novelty by making good what appears to me a deficiency which has hitherto obtained in the matter of pictorial illustration. In particular, there will be found a tolerably extensive series of woodcuts, serving to represent the more important products of artificial selection. These, like all the other original illustrations, have been drawn either direct from nature or from a comparative study of the best authorities. Nevertheless, I desire it to be understood that the first part of this treatise is intended to retain its original character, as a merely educational exposition of Darwinian teaching—an exposition, therefore, which, in its present form, may be regarded as a compendium, or hand-book, adapted to the requirements of a general reader, or biological student as distinguished from those of a professed naturalist.

The case, however, is different with the second instalment, which will be published at no very distant date. Here I have not followed with nearly so much closeness the material of my original lectures. On the contrary, I have had in view a special class of readers; and, although I have tried not altogether to sacrifice the more general class, I shall desire it to be understood that I am there appealing to naturalists who are specialists in Darwinism. One must say advisedly, naturalists who are specialists in Darwinism, because, while the literature of Darwinism has become a department of science in itself, there are nowadays many naturalists who, without having paid any close attention to the subject, deem themselves entitled to hold authoritative opinions with regard to it. These men may have done admirable work in other departments of natural history, and yet their opinions on such matters as we shall hereafter have to consider may be destitute of value. As there is no necessary relation between erudition in one department of science and soundness of judgment in another, the mere fact that a man is distinguished as a botanist or zoologist does not in itself qualify him as a critic where specially Darwinian questions are concerned. Thus it happens now, as it happened thirty years ago, that highly distinguished botanists and zoologists prove themselves incapable as judges of general reasoning. It was Darwin’s complaint that for many years nearly all his scientific critics either could not, or would not, understand what he had written—and this even as regarded the fundamental principles of his theory, which with the utmost clearness he had over and over again repeated. Now the only difference between such naturalists and their successors of the present day is, that the latter have grown up in