to a very great extent, upon Müller's own discoveries. The "Handbook of Physiology" was accepted with almost universal accord as the most valuable treatise on general physiology that had appeared in the long interval since the time of Haller. It is perhaps of interest to observe that these two writers have much in common, for in both we perceive the fundamental desire of placing the doctrine of physiology upon a basis of fact. Anatomy, human and comparative, experiments on animals, chemistry and physiological science in its various departments, are all called in to bear upon the investigation of the truths of physiology. As one of his commentators has remarked, Müller in this work, as in his others, takes nothing on trust; every statement, whether matter of fact or of doctrine, is thoroughly tested; difficulties, however perplexing, are never evaded or slurred over; defects, however much they may deface the picture to be presented, are never disguised. The result of each quest, whether success or failure, is honestly told and there is no yielding to the temptation, so powerful with writers of systems, "to round off a ragged subject with smooth plausibilities." The influence of the "Handbook" was immense, and the judgment of it appears to have been conditioned not alone by the physiological data it contained, but also by the collected facts of importance to the medical profession.
With the completion of the "Handbook," Müller's activity in this particular line of work seems to have practically ended. From this time on he engaged himself to a greater extent in the fields of comparative anatomy and zoology; and in these subjects, as also in his physiology, Müller excelled both in the abundance of his observations and in the wide range of his discoveries. In his work on the comparative anatomy of the myxinoid fishes, Müller lays down the morphological plan of the vertebrates in their simplest form. The title conveys but a faint notion of the scope of this work. Although it treats chiefly of the anatomy of this particular family of fishes, it is rich in new and original matter in which the structure is compared with that of other families of fishes, and the facts sagaciously applied to the elucidation of greater questions in animal morphology. Regarding Müller's study of the Echinoderms, we may quote from an address by the president of the Royal Society of London: