ON THE GENETIC VIEW OF NATURE. 303 



of his contemporaries which Darwin did, and for 

 which he indeed largely prepared the way. Instead 

 of opposing the genetic change and development of 

 the forms of natural objects to their apparent fixity, 

 he rather reconciled both views with each other by 

 maintaining 1 " that in order to obtain a just insight 

 into the mutual affinities of animals it is before all 

 things necessary to distinguish the different types of 

 organisation from the different grades of development." 

 He considered that 2 " the idea of animal organisation 

 does not vary at equal intervals, but is realised in 

 certain principal forms which again break up into 

 variations of a lower grade " ; and he 3 " arrived at the 

 four principal divisions of the animal kingdom estab- 

 lished by Cuvier." In 1828, in his work on the 'De- 

 velopment of Animals,' he discusses 4 " the prevalent 

 notion that the embryo of higher animals passes through 

 the permanent forms of the lower animals " i.e., " the 

 doctrine of the agreement of individual metamorphosis 

 with the ideal metamorphosis of the whole animal 

 kingdom." Von Baer had himself added greatly 5 to 



1 See Huxley's translation, loc. results : " It was von Baer who 

 cit, , p. 178. first clearly discriminated the great 



2 Ibid., p. 182. events in a life-history ; (a) the 



3 Ibid., p. 183. 



4 See K. E. von Baer's ' Ueber 

 Entwickelungsgeschichte der Thiere 

 Beobachtung und Reflexion, 'Konigs- 

 berg, 1828. The above extracts 



primary process of egg-cleavage, 

 and the establishment of the 

 germinal layers ; (6) the gradual 

 differentiation of the tissues (his- 

 togenesis) ; and (c) the blocking 



are taken from the fifth scholion : i out "of the organs (organogenesis), 



" Ueber das Verhaltniss der Formen, : and the shape- taking of the entire 



die das Individuum in den verschie- j organism (morphogenesis) (' Science 



denen Stufen seiner Entwickelung of Life,' p. 123). The classical 



annimmt. " See also Huxley's 'work of von Baer is dedicated to 



Translation, loc. cit., pp. 186, 189. his friend Pander, from whom and 



5 Prof. J. A. Thomson sum- Dollinger he acknowledges having 



marises as follows von Baer's own received the first impulses towards 



