282 DRIESCH'S THEORIES OF DEVELOPMENT V 



with the normal development of the larva ; they are all equiva- 

 lent, without limit, at least until the ectoderm and endoderm have 

 been differentiated ; any part can contribute to the formation of 

 any organ : ' jeder Theil kann jedes.' 



This conception, of the absolute equipotentiality of the parts, 

 as we have already had occasion to remark, is erroneous ; but 

 for Driesch it is of the first importance, for it dominates, as we 

 shall see, all his theoretical speculations. 



The position of the embryonic axes and primary organs being 

 thus determined in the whole egg (or its isolated parts), it is still 

 left to inquire into the causes which decide the destinies of the 

 remainder. Driesch's answer to this question is twofold : there 



FIG. 166. Diagram to illustrate the possible part played by stimuli 

 ('inductions') in ontogeny, and by 'position'. A, B, and C are three 

 larval organs (ectoderm, endoderm, stomodaeum). C may exert a stimulus 

 on that part of B nearest it ; this part, reacting to the stimulus, 

 becomes p. Were the position of C altered the position of /3 in the 

 equipotential system B might be altered too, so that the fate of any 

 part of B would be a function of its position relative to C. So, under 

 the influence of B, part of A may become a. (After Driesch, 1894.) 



are two possible factors, one is ' position ', the other ' induction '. 

 In the case of the first, the destiny of a part is imagined to be 

 determined by its distance from the system of points already 

 established, ' its fate/ so runs the famous formula, ' is a function 

 of its position in the whole.' It would, however, be absurd to 

 suppose that the behaviour of any one of a number of precisely 

 similar bodies could depend upon its mere geometrical position. 

 The points already differentiated the animal pole, for instance 

 must be supposed to exert an influence with a force which is 

 some function of the distance upon the parts which are at present 

 equivalent, and so to excite their differentiation (Fig. 166). 



