organism, and among its qualities as an organism is the power of growth by assimilating material different from itself. Yet, in spite of this assimilation and constant change, it grows and decays as one whole and reproduces its like. Another point of analogy between the animate and the inanimate sphere is that the process of study in both has been from the larger to the smaller elements. The microscope has played at least as decisive a part as the telescope, and it dates from about the same time, at the beginning of the seventeenth century. Since then it has penetrated farther and farther into the infinitesimal elements of life and matter, and in each case there seems to be no assignable limit to our analysis. The cell is broken up into physiological units to which almost every investigator gives a new name. We are now confronted by the fascinating theory of Arrhenius of an infinite universe filled with vital spores, wafted about by radio-activity, and beginning their upward course of evolution wherever they find a kindly soil on which to rest. To such a vision the hopes and fears of mortal existence, catastrophes of nature or of society, even the decay of man, seem transient and trivial, and the infinities embrace. A third point, perhaps the most important in the comparison, is the way by which the order of science has entered into our notions of life, through a great theory, the theory of evolution or the doctrine of descent. In this we find a solid basis for the co-ordination of facts: it was the rise of this theory in the hands of one thinker of unconquerable patience and love of truth which has put the study of biology in the pre-eminent position which it now holds. But it is necessary to consider the evolution theory as something both older and wider than Darwin's presentation of it. Darwin's work was to suggest a _vera causa_ for a process which earlier philosophers had imagined almost from the beginning of abstract thought. He observed and collected a multitude of facts which made his explanations of the change of species--within their limits--as convincing as they are plausible. But the idea that species change, by slow and regular steps, was an old one, and his particular explanations, natural and sexual selection, are seen on further reflection to have only a limited scope.