122 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



The " Harmonious -Equipotential System '' 



We have an ectoderm of the gastrula of a starfish here 

 before us ; we know that we may cut off any part of it in 

 any direction, and that nevertheless the differentiation of 

 the ectoderm may go on perfectly well and result in a 

 typical little embryo, which is only smaller in its size than 

 it would normally be. It is by studying the formation of 

 the highly complicated ciliary band, that these phenomena 

 can be most clearly understood. 



Now let us imagine our ectoderm to be a cylinder instead 

 of being approximately a sphere, and let us imagine the 

 surface of this cylinder unrolled. It will give us a plane 

 of two definite dimensions, a and b. And now we have all 

 the means necessary for the analytical study of the differentia- 

 tion of an harmonious-equipotential system. 



Our plane of the dimensions a and b is the basis of the 

 normal, undisturbed development ; taking the sides of the 

 plane as fixed localities for orientation, we can say that the 

 actual fate, the " prospective value " of every element of the 

 plane stands in a fixed and definite correlation to the 

 length of two lines, drawn at right angles to the bordering 

 lines of the plane ; or, to speak analytically, there is a 

 definite actual fate corresponding to each possible value of 

 x and of y. Now, we have been able to state by our experi- 

 mental work, that the prospective value of the elements of 

 our embryonic organ is not identical with their " prospective 

 potency," or their possible fate, this potency being very 

 much richer in content than is shown by a single case of 

 ontogeny. What will be the analytical expression of such 

 a relation? 



