No book of this century has roused such a tempest as _The Origin of Species_. A number of the younger men of science hailed the theory with eagerness, and one or two of the older were extremely friendly; but many were startled and were unprepared to accept views so novel. Still more, the exponents of orthodox religion were wild against the theory; and in the British Association meeting in 1860, at Oxford, Bishop Wilberforce, by an unmannerly attack, drew down upon himself a crushing rebuke from Huxley. Gradually a calmer temper prevailed, and the problems were discussed fairly on both sides, as questions of science, not matters of faith to be determined by an appeal to Genesis. The time has not yet come for a final verdict upon _The Origin of Species_; but even if Darwin's theory should in the end prove to need great modification, his book will still be one of first-rate importance. It has proved itself already the most stimulating book of the century. Those who oppose Darwin oppose him now with his own weapons: they are evolutionists, though they think some other scheme of evolution the true one. The change is vast from the almost universally prevalent belief in special acts of creation and fixed types to a belief, nearly as widespread, in the gradual development of all the variety of life from at most a few primordial forms. And this result has been, more than almost any result equally great, the work of one man. This great book was followed by some of those special studies which Darwin had the gift of making almost as interesting as his discussions of central principles. This is partly because he makes all his work illustrative of those principles. No one was ever more steadfastly guided by a single idea; and hence his works have an unusually intimate connexion with one another. Thus, _The Fertilisation of Orchids_ (1862) is a detailed study of a subject which occupies one or two paragraphs in the _Origin_. In _The Movements and Habits of Climbing Plants_ (1865) Darwin broke new ground; for it was after the publication of _The Origin of Species_ that he was led to notice these phenomena. The new material however served the purpose of the theory, and the author was 'pleased to find what a capital guide for observations a full conviction of the change of species is.' The book on climbing plants was the outcome of observations carried on in broken health. 'All this work about climbers,' says Darwin, 'would hurt my conscience, did I think I could do harder work.' In _The Variation of Animals and Plants under Domestication_ (1868), on the other hand, he was reverting to that department of investigation in which he had first seen clear light on the question of species. The most debated point in this book is the celebrated speculation of Pangenesis. Darwin advanced it, not as something proved, but because 'it is a relief to have some feasible explanation of the facts, which can be given up as soon as any better