ON THE GENETIC VIEW OF NATURE. 



297 



grown life, the unification of thought on these matters, is 

 quite as important in the history of science as the abolition 

 of the supposed fundamental difference between animal 

 and vegetable growth or between normal and abnormal (or 

 pathological) development. The reduction of all these 

 seemingly so different changes to the one great problem 

 of cellular structure, cellular growth, and cellular division 

 marks one of the greatest achievements of our century. 

 " Our position with regard to the cell is similar to that 

 of investigators towards the whole animal or vegetable 

 body a hundred years ago, before the discovery of the 

 cell theory." 1 



Anticipations of this generalisation, of the condensation 

 of the whole problem of animal and vegetable embryology, 

 of generation, growth, and organic development in the 

 formula, " omnis cellula ex cellula," have indeed existed 

 since the time of Harvey, who, in addition to the great 

 discovery of the circulation of the blood, laid down the 



thesis, " omne vivum ex ovo. 



2 



The further correct 



1 See 0. Hertwig, "The Cell," 

 ' Outlines of General Anatomy and 

 Physiology.' Transl. by Campbell, 

 1895, p. 11. 



- One of the best expositions of 

 Harvey's ideas is to be found in 

 Huxley's article on " Evolution in 

 Biology " in the ninth edition of 

 the ' Encyclopaedia Britannica.' He 

 there also refers to Aristotle's 

 opinions. "One .of Harvey's prime 

 objects is to defend and establish, 

 on the basis of direct observation, 

 the opinion already held by Aris- 

 totle, that in the higher animals 

 at any rate the formation of the 

 new organism by the process of 

 generation takes place, not sud- 

 denly by simultaneous accretion of 

 rudiments of all, or of the most 



important of the organs of the 

 adult, nor by sudden metamor- 

 phosis of a formative substance 

 into a miniature of the whole, 

 which subsequently grows, but by 

 epigenesis, or successive differentia- 

 tion of a relatively homogeneous 

 rudiment into the parts and struc- 

 tures which are characteristic of 

 the adult." In the sequel of his 

 exposition, after maintaining epi- 

 genesis or after-formation against 

 evolution in the older sense or pre- 

 formation, Huxley, however, makes 

 a passing remark that " though the 

 doctrine of epigenesis, as understood 

 by Harvey, has definitely triumphed 

 over the doctrine of evolution, . . . 

 it is not impossible that, when the 

 analysis of the process of develop- 



