VITALISM 387 



egg can therefore, according to the needs of the case, give rise 

 to any part of the resulting organism." Now Driesch asserts 

 that although a mechanism might be imagined which will bring- 

 about development within an undivided egg, it is impossible to 

 imagine one which can be subdivided at any point and in any 

 direction and yet remain a complete machine and cause any 

 sufficiently large part to develop into a complete organism. It 

 may be that Driesch is mistaken in his denial of this possibility, 

 for a magnet can be divided in various ways and each part will 

 still be a magnet but the answer commonly given is not of this 

 nature and has already been met by Driesch himself. Dr. 

 Jenkinson, for example, writes : 



" The reply to this contention is simple. It is not true that 

 the development capacity of every part of the germ is so un- 

 restricted. For experiment has taught us, first, that there are 

 in the unfertilised ovum certain different substances, definitely 

 and necessarily connected with the development of certain 

 organs, since their removal entails the absence of the organ to 

 which each is appropriate ; secondly (and here some of the 

 evidence has been brought forward by Driesch himself), that in 

 the process of segmentation a time always comes when these 

 substances become allocated to the several cells and that there- 

 after the potentialities of those cells are limited. At what 

 particular moment that limitation occurs depends on the 

 original arrangement of the substances in the ovum, which is 

 variable. Only so long as each cell contains a sample of each 

 substance does it retain the capacity for total development." 



All this of course is perfectly true but as Driesch has 

 pointed out, it does not invalidate his argument. In some eggs 

 the " organ-forming " substances are definitely arranged at the 

 time of laying, in others they are more or less uniformly dis- 

 tributed and only become localised during development. But 

 the point of Driesch's contention is that their localisation 

 cannot be the work of a machine contained within the egg, 

 if that machine can be subdivided in any possible manner and 

 yet remain capable of doing its work to perfection. In some 

 cases the work of arrangement is done before the egg is laid, in 

 others only during the early development of the embryo ; but 

 the presence of substances necessary for the formation of certain 

 parts is no more proof of the existence of a machine than the 

 presence of separate piles of bricks, stones, wood, etc., where a 

 house is to be built is a proof that the house is put together 



