embryology he gratefully acknowledges his debt to his old teacher. "Among the most fascinating of our professors was Oken. A master in the art of teaching, he exercised an almost irresistible influence over his students. Constructing the universe out of his own brain, deducing from a priori conceptions all the relations of the three kingdoms into which he divided all living beings, classifying the animals as if by magic, in accordance with an analogy based on the dismembered body of man, it seemed to us who listened that the slow laborious process of accumulating precise detailed knowledge could only be the work of drones, while a generous, commanding spirit might build the world out of its own powerful imagination. The temptation to impose one's own ideas upon nature, to explain her mysteries by brilliant theories rather than by patient study of the facts as we find them, still leads us away. With the school of the physio-philosophers began (at least in our day and generation) that overbearing confidence in the abstract conceptions of the human mind as applied to the study of nature, which still impairs the fairness of our classifications and prevents them from interpreting truly the natural relations binding together all living beings. And yet, the young naturalist of that day who did not share, in some degree, the intellectual stimulus given to scientific pursuits by physio-philosophy would have missed a part of his training. There is a great distance between the man who, like Oken, attempts to construct the whole system of nature from general premises and the one who, while subordinating his conceptions to the facts, is yet capable of generalizing the facts, of recognizing their most comprehensive relations. No thoughtful naturalist can silence the suggestions, continually arising in the course of his investigations, respecting the origin and deeper connection of all living beings; but he is the truest student of nature who, while seeking the solution of these great problems, admits that the only true scientific system must be one in which the thought, the intellectual structure, rises out of and is based upon facts. The great merit of the physio-philosophers consisted in their suggestiveness. They did much in freeing our age from the low estimation of natural history as a science which prevailed in the last century. They stimulated a spirit of independence among observers; but they also instilled a spirit of daring, which, from its extravagance, has been fatal to the whole school. He is lost, as an observer, who believes that he can, with impunity, affirm that for which he can adduce no evidence. It was a curious intellectual experience to listen day after day to the lectures of Oken, while following at the same time Schelling's courses, where he was shifting the whole ground of his philosophy from its negative foundation as an a priori doctrine to a positive basis, as an historical science. He unfolded his views in a succession of exquisite lectures, delivered during four consecutive years. "Among my fellow-students were many young men who now rank among the highest lights in the various departments of science, and