290 DRIESCH'S THEORIES OF DEVELOPMENT V 



differentiation is resolved is held to result from the initial 

 structure of the germ and to be maintained by the constitution 

 of the environment. Now, however, it is urged that no materia 

 factor can possibly account either for this harmony or for the 

 secondary harmony of composition or the functional harmony 

 seen in the activities of the adult. When, for example, the 

 gastrula of a sea-urchin is transversely divided into two, each 

 develops into a diminished whole larva in which the gut 

 becomes divided into the characteristic three regions, and all the 

 other organs are formed in correct proportion. For each of these 

 acts in the whole uninjured larva an explanation may conceivably 

 be given in terms of stimuli or forces emanating from the 

 originally distinct parts of the egg and producing effects which 

 vary with the distance upon other parts, as suggested before. 

 A mechanism may be thought of which, when set in motion, 

 will achieve a certain end in accordance with its own pre-estab- 

 lished harmony, but a mechanism which can be subdivided ad 

 libitum, or almost ad libitum., and the parts of which will still 

 achieve the same end, will still behave as wholes with their parts 

 co-ordinated in the same ratio, temporally and spatially ! Such 

 a mechanism is an inconceivability, for to ensure the result 

 which does happen the working distance of the forces imagined 

 must be altered in each case according to the size of the fragment 

 removed. Something is therefore required to superintend, to 

 co-ordinate, to harmonize the causes of development in the case 

 not only of the part but of the whole egg as well ; and this 

 something is not material. A corroborative proof of the inad- 

 equacy of the purely material explanation the causal explanation 

 in the ordinary sense of the word may be derived from a con- 

 sideration of certain other vital processes. The facts of acclimati- 

 zation and immunity betray an extraordinary adaptability of 

 the organism to a change in its environment; an organ will 

 adapt itself structurally to an alteration, quantitative or qualita- 

 tive, of function (Roux's ' functional adaptation '} ; lost parts can 

 be regenerated ; and then there is the physiology of the nervous 

 system ! 



In all these cases of ' regulation ' and indeed in all other 

 responses to stimuli the same element, inexplicable in chemical 



