genius often prove to be leaps through the dark into great discoveries. As examples of Darwin's writings I have chosen, in addition to those already mentioned, certain passages from his great book on the 'Origin of Species,' in which he explains what he understands by the terms "Natural Selection" and the "Struggle for Existence." These terms invented by Darwin--but specially the latter--have become "household words." The history of his thoughts on the subject of the Origin of Species is given in the account of his books, written by himself and already referred to. His letter to Professor Asa Gray (September 5th, 1857) is a most valuable brief exposition of his theory and an admirable sample of his correspondence. The distinguished American botanist was one of his most constant correspondents and a dear personal friend. I have also given as an extract the final pages of the 'Origin of Species,' in which Darwin eloquently defends the view of nature to which his theory leads. A similar and important passage on the subject of 'Creative Design' is also given: it is taken from that wonderful collection of facts and arguments published by Darwin under the title of 'The Variation of Plants and Animals under Domestication.' It cannot be too definitely stated, as Darwin himself insisted, that his theory of the Origin of Species is essentially an extension of the argument used by Lyell in his 'Principles of Geology.' Just as Lyell accounted for the huge masses of stratified rocks, the upheaved mountain chains, the deep valleys, and the shifting seas of the earth's surface, by adducing the long-continued cumulative action of causes which are at this present moment in operation and can be observed and measured at the present day: so Darwin demonstrates that natural variation, and consequent selection by "breeders" and "fanciers" at the present day, give rise to new forms of plants and animals; and that the cumulative, long-continued action of _Natural_ Selection in the Struggle for Existence, or the survival of favorable variations, can and must have effected changes, the magnitude of which is only limited by the length of time during which the process has been going on.