322 THE PHILOSOPHY OF BIOLOGY 



of necessity to a different final phase, but a change in 

 the conditions under which the embryo develops need 

 have no such effect. If some unforeseen occurrence 

 takes place — some artificial interference with the 

 process of segmentation, which could never have been 

 experienced in the racial history of the organism — a 

 regulation by the parts of the embryo occurs, and the 

 final phase of development may be the same as if no 

 interference had been experienced. That which is 

 operating in the development of the embryo is some- 

 thing that is permitting, or suspending, or arranging 

 physico-chemical reactions. 



Let us think of the developing embryo merely as an 

 aggregation of substances contained in an inorganic 

 medium : the segmented frog's egg floating on the 

 water at the surface of a pond is an example. As an 

 inorganic system its fate is determined. Autolysis of 

 the substances in the cells will occur and the proteids 

 will break down with the formation of amido-bodies, 

 while other chemical changes, strictly predictable if 

 our knowledge of organic chemistry were more complete 

 than it is, would also occur. Putrefactive and fermen- 

 tative bacteria will attack the proteids, fats, and carbo- 

 hydrates, and in the end our aggregation of chemical 

 substances will become an aggregation of much simpler 

 compounds — water, carbon dioxide, marsh gas, sulphur- 

 etted hydrogen, phosphoretted hydrogen, ammonia, 

 nitrates, etc., all of which will dissolve in the water of 

 the pond, or will diffuse into the adjacent atmosphere. 

 But in the living embryo this is not what occurs : an 

 entirely different, and much more complex, arrange- 

 ment of the chemical substances originally present in 

 the segmented egg, or at least a physical and chemical 

 re-arrangement, is brought about. The entelechy of 

 the developing embryo prevents some reactions from 



