MODERN BIOLOGY 531 



During his short life he found time to carry out a number of extremely 

 important works on evokition, including a study of the evolution of the 

 sharks and a Treatise of Comparative Embryology, giving an account of the evo- 

 lution of the Q.gg and the embryo throughout the animal kingdom, a work 

 that was of unrivalled importance at the time; an application of modern 

 genetical embryology to the whole animal kingdom and at the same time 

 a powerful defence of the Darwinian morphology in its classical form. Bal- 

 four, in fact, definitely maintains that phylogeny is the goal of evolution, 

 while at the same time in certain details, as, for instance, in the theory of 

 extremity-formation previously mentioned, he adopts a dissentient attitude 

 towards the contemporary Gegenbaur school. 



Even by then the morphogenetical embryology had met with decided 

 opposition on the part of the naturalists who desired to substitute for phy- 

 logenetical conclusions the study of function in those organs whose evolu- 

 tion was under investigation, and thus to give evolution a more or less 

 physiological direction. To this group belongs the afore-mentioned Wil- 

 HELM His (1831-1904), who was born at Basel, became professor of anatomy 

 there, but was afterwards summoned to Leipzig, where he worked until his 

 death. Famous both as an anatomist and as an embryologist, he paved the 

 way for a new line of research, particularly in the field of embryology. First 

 of all he expected to see in the evolution of the embryo a physiological 

 process, the course of which should be so studied that each later stage of 

 development must necessarily proceed from the immediately preceding one. 

 The changes whereby the simple egg-cells are formed into complex organisms 

 are, to his mind, purely mechanical; as the result of a series of flexions, 

 fold-formations, and accretions the embryo arises out of the originally 

 lamellate germinal layers, and its folds are in their turn produced entirely 

 from variformed growth. Every organ possesses its given rudiments in the 

 germinal layers and these layers thus consist of a quantity of " organbildende 

 Keimbex.irke" ; they are therefore not indifferent, as C. F. Wolff and, after 

 him, Haeckel declared. In connexion herewith His sharply criticizes the 

 biogenetical principle; embryos of different animal forms are as easily dis- 

 tinguishable from one another as the fully developed animals; Haeckel 's 

 proofs to the contrary, both verbal and pictorial, are examined and found 

 to be untenable, and finally the question is put: "If we possessed a complete 

 genealogical tree, would our own or any other extant organic form be fully 

 explained thereby?" In reply His declares that if in a case of near-sightedness 

 it is possible to establish the fact that the individual in question has inherited 

 the defect, little will have been gained therefrom as regards our knowledge 

 of the character of that defect; rather, the eye's capacity for accommodation 

 and other concomitant circumstances must be investigated for this purpose; 

 in the same way, the physiological side of embryonic development is more 



