124 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



the prospective value of every element of the two pieces cut 

 out of the germ may vary even in relation to the direction 

 of the cut itself. Our element, X, may belong to both of 

 these pieces of the same size : its actual fate nevertheless 

 will be different. Analytically, it may be said to change in 

 correspondence to the actual position of the actual boundary 

 lines of the piece itself with regard to the fundamental lines 

 of orientation, a and & ; let this actual position be expressed 

 by the letter I, I marking the distance of one 1 of the actual 

 boundary lines of our piece from a or I : then we are entitled 

 to improve our formula by writing p.v. (X) =/ (s, I . . . ) 

 (Fig. 11). 



But the formula is not yet complete : s and I are what 

 the mathematicians call variables : they may have any 

 actual value and there will always be a definite value of p.v., 

 i.e. of the actual fate which is being considered ; to every 

 value of s and I, which as we know are independent of 

 each other, there corresponds a definite value of the actual 

 prospectivity. Now, of course, there is also a certain factor 

 at work in every actual case of experimental or normal 

 development, which is not a variable, but which is the same 

 in all cases. This factor is a something embraced in the 

 prospective potency of our system, though not properly 

 identical with it. 



The prospective potency of our system, that is to say of 

 each of its elements, is the sum total of what can be done 

 by all ; but the fact that a typically proportionate develop- 

 ment occurs in every possible case, proves that this sum 

 comes into account, not merely as a sum, but as a sort of 



1 The distance of the other boundary line from a or b would be given by 

 the value of s. 



