Several months ago I published in the Fortnightly Review a lecture, which I had previously delivered at the Philosophical Institutions of Edinburgh and Birmingham, and which bore the above title. The late Mr. Darwin thought well of the epitome of his doctrine which the lecture presented, and urged me so strongly to republish it in a form which might admit of its being ''spread broadcast over the land'', that I promised him to do so. In fulfilment of this promise, therefore—which I now regard as more binding than ever—I reproduce the essay in the ''Nature Series'' with such additions and alterations as appear to me, on second thoughts, to be desirable. The only object of the essay is that which is expressed in the opening paragraph.
ther series of facts in the physical universe.
This being understood, I shall now proceed to render an epitome of the evidence in favour of organic evolution, and I shall do so by classifying the arguments in a way tending to show their distinct or independent character, and therefore calculated to display the additional force which they acquire from their cumulative nature.
THE ARGUMENT FROM CLASSIFICATION.
I shall first take the argument from classification. Naturalists find that all species of plants and animals present among themselves structural affinities. According as these structural affinities are more or less pronounced, the various species are classified under genera, orders, families, classes, sub-kingdoms, and kingdoms. Now in such a classification it is found impossible to place all the species in a linear series, according to the grade of their organization. For instance, we cannot say that a wolf is more highly organized than a fox or a jackal; we can only s