MODERN BIOLOGY 399 



at the time — he believed that the separate granules in the yolk of the egg 

 are independent cells — but nevertheless with great accuracy in his obser- 

 vations of the consecutive stages of development, resulting in his establishing 

 the cell character of the products of division, out of which the embryo is 

 formed. Even the two afterwards oft-recurring expressions "BiUungs-" and 

 "Nahrungsdotter" originate from him. One or two works on the evolution 

 of the tadpole likewise contain sound observations; one of them contains a 

 number of general reflections on the subject of organic formation by means 

 of invagination, which in a certain degree foreshadowed Haeckel's gastra^a 

 theory. Reichert's greatest contribution, however, lies in his study of the 

 evolution of the connective substance; he introduced this term to imply a 

 number of connecting-tissue elements of different structure and has based 

 it upon arguments from evolutional history. In his old age Reichert was com- 

 pletely isolated; he refused to accept the new protoplasm theories, and still 

 more the origin-of-species theory, and he made no attempt to hide his disgust 

 when these ideas prevailed. In particular, he attacked with great vehemence 

 Haeckel's theory of the germ layers being homologous throughout the ani- 

 mal kingdom; instead, he maintained the independent origin of the separate 

 organs. While he was scorned by Haeckel and his contemporaries, Reichert 

 has to a certain extent been justified by the results of modern research, where- 

 on we shall have more to say in a later chapter. 



Robert Remak was born at Posen in 181 5. Like Henle, he was of Jewish 

 extraction, but in contrast to him held to the faith of his fathers. After 

 studying under Miiller he became his assistant lecturer, eventually being 

 given the honorary title of professor, though never holding a post as or- 

 dinary professor. He made a living by carrying on a medical practice, and 

 this gradually diverted him from a scientific career. He died in 1865. His 

 contribution in the field of cell research is concerned partly with neurology 

 and partly with embryology. Thus, he discovered and described the sym- 

 pathetic nerve fibres called after him, and he established the fact that in the 

 embryonic life the nerves are constructed in the form of fibres which grow out 

 from the nerve-cells. He is specially worthy of remembrance, however, for the 

 determined opposition he made to Schwann's theory of free cell-formation; 

 he studied the evolution of frogs' eggs and thereby proved that the egg is a 

 cell that divides itself up into new cells and that this division starts from the 

 nuclei; he does not accept any cell-formation by accumulation in a formless 

 matter. Further he drew a comparison between the embryonic development 

 in the egg of the frog and in that of a bird: it was he who invented the terms 

 "holoblastic" and "meroblastic," which are still used for these two types 

 of egg. He distinguishes three germinal layers, which he believes to be com- 

 mon to the embryonic development of all vertebrates and which giwe rise, 

 the outermost to the nervous system, the middlemost to the musculature, 



