When we find Haeckel intimate in this way with Gegenbaur, his senior by eight years, we realise how close he was at that time to the whole of the Würtzburg circle. The two generations were not yet sharply divided, as they subsequently were. Most of them fought either with or against him at a later date, but they belonged, at all events, to the same stratum. But the split between the two generations was felt when one pronounced the name of Johannes Müller, of Berlin—the physiologist (not the historian). All who then taught histology, embryology, comparative anatomy, or cellular pathology at Würtzburg had sat at his feet, either spiritually or in person. Johannes Müller, born at the beginning of the century, was appointed Professor of Anatomy and Physiology at Berlin the year before Haeckel was born. That indicates the distance between them. It was in Müller’s incredibly primitive laboratory that, as Haeckel tells, the theory of the animal-cell was established by his assistant, Theodor Schwann, after Schleiden had proved the vegetal cell. Müller himself had founded histology in his own way. He was the real parent of the idea that the zoologist ought to go and work by the sea. We have a model of this kind of work and at the same time a superb work for embryological matters in Müller’s epoch-making _Studies of the Larvæ and Metamorphoses of the Echinoderms_. He had brought comparative anatomy beyond the stage of Cuvier, to a point where Gegenbaur could begin. From his school came Rudolf Virchow, who applied the cell-theory to medicine, and Emil du Bois-Reymond, who opened out a new path in physiology by his studies of animal electricity. Müller had done pioneer work with remarkable vigour in all the various branches of research, diverging afterwards to an enormous extent, that pursue these methods. The many-headed (young and half-young) generation, in which Haeckel was growing, saw the whole previous generation embodied in the single name of Müller. He seemed to be a kind of scientific Winkelried, except that the fifty spears he bore on his breast were so many lines of progress emanating from him alone. Johannes Müller had the great and splendid gift of never lying on the shoulders of his pupils with an Alpine weight of authority. It was a secret of his personality that we admire but can hardly express in words to-day. Everybody learned from him what a great individuality is. He exerted a kind of moral suggestion in teaching men to be free, great, enlightened, and true. His pupils have worked at the development of his ideas with absolute freedom. No part of them was to be regarded as sacred, and, as a matter of fact, in the chief questions no part has remained.