time: the refreshing river 



error is an example of what I have termed the fallacy of misplaced 

 concreteness." 



To the biologist all this was extremely welcome. If for three 

 hundred years he had been a "mechanist" following in the footsteps 

 of Descartes and la Mettrie, it was not because he felt satisfied with 

 the seventeenth-century statistical picture of the fortuitous con- 

 course of particles, each with a momentarily defined exact position 

 in space, but because there was no other scheme by the aid of which 

 he could proceed with the causal analysis of biological phenomena. 

 The difficulties rose, of course, to a wild crescendo in the science of 

 embryology at the turn of the century. When experimental embryology 

 was put on a firm foundation by Wilhelm Roux, it was supposed 

 that all eggs showed what is called "mosaic" development, that is to 

 say, they would, if injured or divided, produce a finished organism 

 lacking precisely all that would have developed from those parts 

 which had been destroyed or removed. About 1895, however, the 

 discovery was made (and this is what has secured Hans Driesch's 

 name in history, not what he wrote long aftei-wards) that in many 

 eggs, at any rate, all kinds of interferences could be made without 

 affecting at all the embryo resulting. Large pieces could be removed 

 from the egg, several blastomeres could be taken away, or the blasto- 

 meres could be shuffled at will, and yet a normal, though small- 

 sized, embryo would result. Any one monad in the original egg-cell, 

 then, was capable of forming any part of the finished embryo. Driesch 

 was quite right in proclaiming that this was beyond the powers of 

 any machine such as man has ever constructed, but he soon left the 

 straight and narrow path by insinuating his non-material entelechy 

 into the works as the inevitable transcendent mechanic or driver. C. D. 

 Broad's comment deserves to be better known: "If you want a mind 

 that will construct its own organism, you may as well postulate God 

 at once. If He cannot perform such a feat, it is hardly likely that what 

 has been hidden from the wise and prudent will be revealed to en- 

 telechies."! 



Looking at the matter to-day after the passage of forty years 

 of research in experimental morphology, we realise that what these 

 early workers were up against was a very general process in develop- 

 ment which we now speak of as Determination.^ The individual 



^ C. D. Broad, Proc. Aristot. Soc, 1919, 19, 123. 



^ As the new concepts came in in embryology, the old apparent necessity for pos- 

 tulating non-material factors went out. The process was excellently described by a 



196 



