Several years ago Lord Rosebery founded, in the University of Edinburgh, a lectureship on “The Philosophy of Natural History,” and I was invited by the Senatus to deliver the lectures. This invitation I accepted, and subsequently constituted the material of my lectures the foundation of another course, which was given in the Royal Institution, under the title “Before and after Darwin.” Here the course extended over three years—namely from 1888 to 1890. The lectures for 1888 were devoted to the history of biology from the earliest recorded times till the publication of the “Origin of Species” in 1859; the lectures for 1889 dealt with the theory of organic evolution up to the date of Mr. Darwin’s death, in 1882; while those of the third year discussed the further developments of this theory from that date till the close of the course in 1890.