The naturalist whose memory is being honored to-day over the whole civilised world must be ranked as among the greatest--perhaps the very greatest--of all scientific discoverers. One other--Sir Isaac Newton--can alone be compared with him. Both had the same characteristics of great reasoning power, immense industry, and extreme patience in elaborating the proofs of their respective theories; and it is a curious coincidence that in both cases twenty-one years were allowed to elapse between the conception of the new idea and its publication, with elaborated proofs.

     No one can properly understand the greatness of Darwin's work in modifying the thought of the whole scientific world who does not know something of the state of opinion when he was developing his theory. This may be shortly described as an almost universal belief in the stability of species, a very general acceptance of the doctrine of "special creation," and a contempt, often amounting to moral condemnation, of all who held contrary views.

     The ingrained prejudice on this subject, though strongest in the religious world, was equally prevalent among the greatest naturalists and men of science of the day; and it is well shown in a letter from Darwin to his intimate friend Dr. (Now Sir Joseph) Hooker while he was engaged in working out his theory eight years after his return from his voyage in the Beagle. He writes: "I have ever since my return been engaged in a very presumptuous work, and I know no one individual who would not say a very foolish one. . . . At last gleams of light have come, and I am almost convinced that species are not (it is like confessing a murder) immutable. . . . I have found out (here's presumption!) the simple way by which species become exquisitely adapted to various ends. You will now groan, and think to yourself, 'On what a man have I been wasting my time, and writing to.'"

     At the present day this seems exaggerated and almost incredible, but it well reflects the opinion of that time in regard to the very idea of the "transmutation of species," which was held to be scientifically on a par with perpetual motion, and morally with atheism.

     Neither can the value and the convincing power of Darwin's life-work be adequately appreciated by a perusal of his "Origin of Species" alone. He himself termed that work the summary of a summary; and this will not seem exaggerated to anyone who reads carefully his two volumes on "The Variation of Animals and Plants under Domestication," in which is given, in well-arranged sequence, the great mass of facts, observations, and experiments, of which the first chapter of the "Origin" is a very condensed exposition.

     In the interval between these two works appeared the first of a series of volumes on botanical subjects, entitled "On the Various Contrivances by which Orchids are Fertilised by Insects." This book was at once a revelation to botanists and a delight to every lover of nature. It clearly explained the strange forms of most of our native orchises, and the curious, life-like motions of their parts, both exactly adapted to the structure of special insects without whose agency they could not be fertilised or produce seed. An entirely new source of interest was thus given to some of our most curious and beautiful wild flowers, while the many strange forms and gorgeous colours of tropical orchids were shown to have a similar purpose.

"The Descent of Man."

     In 1871 his thick volume on "The Descent of Man, and Selection in Relation to Sex" appeared, and perhaps none of his works has excited more interest or led to more discussion and criticism. It consists really of two separate treatises, which were combined in one volume, because, to complete the work on "Man," he was obliged to discuss the question of external sexual characters, and with his usual thoroughness had first to trace this throughout the entire animal world.

     "The Descent of Man" was written to show that his great principle of "natural selection" served to explain how man had been developed from some lower animal form which was also the ancestor of the various anthropoid apes; and he adduced a large and convincing array of embryological, anatomical, and other arguments showing that he had actually been so descended.

     In this conclusion the great majority of thinkers to-day are in entire agreement with him; but in his further contention--that the whole mental, moral, and aesthetic nature of man has also descended to him from the lower animals--a large and increasing number of his admirers do not follow him, there being at least as much positive evidence against as in favour of his contention.

     As to his conclusions on "Sexual Selection" there is equal diversity of opinion, two quite distinct phenomena being included under the term. These are (1) Weapons used in the combats of the males, which, being clearly useful to them and to the race, have been developed under the law of natural selection; and (2) colours and ornaments in the male sex only, the use of which is not so clear. Here Darwin's contention is that the latter have been developed by the influence of female choice of the most highly ornamented males. The evidence collected by Darwin on this point is so abundant and so extremely interesting that most students were first carried away by it; but further consideration showed that direct evidence for any such choice was very scanty, while there was a fully equal amount against it. The fact that these colours and ornaments were almost equally developed in male butterflies, while it was almost impossible to postulate an identical æsthetic faculty among the females, together with our increasing knowledge of the various ways in which colour is of use, has led to a very general rejection of the theory of female choice.

     In the following year his volume on "Expression of the Emotions in Man and Animals" appeared. This is another highly popular work, dealing largely with domestic animals and children, and offering original and suggestive explanations of their emotional characteristics. The excellent illustrations in this book add greatly to its interest.

     A few years later (in 1876 and 1877) two of his most remarkable botanical works were issued. The first, on "Cross and Self-Fertilisation of Plants," demonstrated the use of cross-fertilisation in increasing vigour and fertility. The second, on "The Different Forms of Flowers in Plants of the Same Species," is devoted to a minute examination and careful series of experiments on our common primrose, cowslip, loose-strife, and other native and exotic plants. These each possess different arrangements and lengths of the stamens and styles, which in the primrose had been long known as the "pin-eyed" and the "thrum-eyed" varieties, and had hitherto been looked upon as mere freaks or abnormalities. But Darwin showed the use and purpose of these peculiarities.

Plants and Worms.

     Three other volumes followed, equally packed with original observation and experiment, and all elucidating phenomena hitherto little understood. These were on "Climbing Plants," "The Movements of Plants," and "Insectivorous Plants," and were of great interest to botanists, while all the facts were elucidated by his great theory.

     Last of all (in 1881, only a year before his death) the reading world was startled and delighted by a volume wholly devoted to the life and habits, the use and place in nature, of the common worm. He showed the benefits of these despised little creatures in improving the earth for vegetation, and that we also owe to them the preservation of the numerous Roman and other remains which delight the archæologist. The subject of this work had been in his mind for forty years, and it records experiments for thirty years on the rate at which worms work.

     A few concluding lines only can be devoted to his character. This was largely inherited from his grandfather, Dr. Erasmus Darwin, and his father, Dr. Robert Darwin. Of his grandfather he writes: "Throughout his letters I have been struck with his indifference to fame and the complete absence of all signs of any overestimate of his own abilities or of the success of his works." And of his father: "His chief mental characteristics were his powers of observation and his sympathy, neither of which I have ever seen exceeded, or even equalled." To these ancestral traits we must add an extreme love of Nature and of all her works, and a high degree of reasoning power which ever led him onward to penetrate her most hidden secrets.

     However far our knowledge of nature may advance in the future, it will be by extending still further the pathways which he has opened for us through the luxuriant jungle of the life-world; and the name of Darwin will ever stand out as the typical example of what the student of nature ought to be. To him even more completely perhaps than to Newton, may be applied the supreme eulogy of the poet:

"Nature and nature's laws lay hid in night,
God said, 'Let Darwin be,' and all was light."