gator since Müller's time. A better conception of the degree of this extraordinary activity may be gained when one considers that Müller, from 1821 (when he was nineteen years old) to the time of his death, thirty-seven years later, produced, year in and year out, an average of one scientific article of from three to five pages, and with from one to three plates, every three weeks. And in none of these do we find the spirit of his work dictated by the desire to show that he could get some sort of a result out of this or that kind of investigation; but rather by the burning desire to survey and to understand the interrelation of all life phenomena.
It would seem that an unconquered field of knowledge left him no rest, and was for him a stimulus to activity just as much as was the knowledge of the existence of an unconquered people to Alexander the Great. At the first opportunity his attention would be directed to it, and never would the field be abandoned until its truths and its principles were at last incorporated in Müller's own system. This, for Müller, meant no simple undertaking. It included the universal proof, the definite transformation, the deepening, the enriching, the building up and the ordering of every detail of the work; so that from each such acquisition the greatest value to science invariably resulted.
This capability of Müller's is shown especially well in his work on the Echinoderms. He early applied himself to the study of the structure and habits of a single group of this interesting branch of animals. From this study he was led to consider the embryonic development, and, finally, having pursued his investigations in this line into four of the five orders of true Echinoderms, he culminated this great work by subjecting the organization of the entire class of Echinoderms, both recent and fossil, to a thorough revision. In this same thorough and exhausting manner, Müller attacked all possible points in the illimitable field of anatomical and physiological knowledge; and the insight into nature, gained through his own exhaustive researches, yielded to him a sureness of judgment which seldom failed him in the decisive moments of his career. An accurate personal knowledge lay at the bottom of his every work.
In the period of his greatest activity, when he was working simultaneously upon "The Development of the Reproductive Organs," "The Development of the Glands," and also the first volume of his "Handbook of Physiology," together with papers on "Osteology" and "The Myology of the Myxinoid Fishes," he must have possessed the ability to profitably divide his interest and to oscillate with a remarkable ease between these several objects of thought and investigation. The result is perhaps still more marvelous when we realize that, as a rule, Müller went over the same line of investigation three times: the second time while he was writing his results, and the third time when