JOHANNES MULLEB 519 



to a very great extent, upon Muller's own discoveries. The " Hand- 

 book 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 depart- 

 ments, are all called in to bear upon the investigation of the truths 

 of physiology. As one of his commentators has remarked, Muller 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 medi- 

 cal profession. 



With the completion of the " Handbook," Miiller'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 com- 

 parative anatomy and zoology; and in these subjects, as also in his 

 physiology, Muller excelled both in the abundance of his observations 

 and in the wide range of his discoveries. In his work on the com- 

 parative anatomy of the myxinoid fishes, Muller lays down the mor- 

 phological 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. Ee- 

 garding Miiller's study of the Echinoderms, we may quote from an 

 address by the president of the Eoyal Society of London : 



Professor Muller early applied himself to the study of the structure and 

 economy of the Echinoderms. After describing in a special memoir the 

 anatomy of Pentacrinus, so interesting as a living representative of the extinct 

 Crinoidea, and publishing, in conjunction with M. Troschel, a systematic ar- 

 rangement and description of the Asteridea, he was at length happily led to 

 investigate the embryo life of this remarkable class of animals. The field of 

 inquiry upon which he entered had scarcely been trenched upon before, and he 

 has since made it almost wholly his own by persevering researches carried on 

 at the proper seasons of the last nine years, on the shores of the North Sea, 

 Mediterranean and Adriatic. In this way he investigated the larval conditions 

 of four out of the five orders of true Echinoderms, and has successfully sought 

 out and determined the commonplace followed in their development, amidst 



