The extent to which Ernst Haeckel was hated and attacked by reactionary scientists, philosophers, litterateurs and preachers, is, as Lenin has pointed out in his “Materialism and Empirocriticism,” a measure of the success with which he originally expounded the results of natural science and drove them home to their logical conclusions in the interpretation of nature on a materialistic basis. Haeckel, in the days of his greatest mental vigor, made himself the spearhead of the scientific attack upon the then dominant forces of theology and obscurantism, showing fearlessly how revolutionary were the results of modern science, and particularly those concerned with evolution, in altering fundamentally man's outlook upon the world in which he lived and his own nature. It has become the mode among many intellectual circles in Western countries to refer slurringly both to the more technical scientific work and to the more general reasoning of Haeckel, as being crude and out of date; but this derogation has its origin in the despair of the teleologists and is not founded in the facts of modern scientific development. Certainly, so far as genetics is concerned, the most modern results are not merely in harmony with, but brilliantly confirmatory of, those main tenets of Haeckel's general interpretation of nature which involved him in the bitterest controversy. In addition they help to show the general soundness of his more technical zoological contributions. By contrast, Haeckel's deficiencies in the realm of social affairs stand out the more strongly, although his own materialism of natural science is a necessary basis for an adequate social materialism. We will not concern ourselves here, however, with Haeckel's own social theories, but only with those in the field of natural science; it was only in the latter field that he attained his real prominence.