EXPERIMENTAL MORPHOGENESIS 83 



saying : though ectoderm and endoderm have their potencies 

 equally distributed amongst their respective cells, they possess 

 different potencies compared one with the other. And the 

 same relation is found to hold for all cases of what we call 

 elementary organs : they are " equipotential," as we may say, 

 in themselves, but of different potencies compared with each 

 other. 



Explicit and Implicit Potencies : Primary and Secondary 



Potencies 



We shall first give to our concept of " prospective 

 potency " a few words of further analytical explanation with 

 the help of our newly obtained knowledge. 



It is clear from what we have stated that the prospective 

 potencies of the ectoderm and of the endoderm, and we may 

 add, of every elementary organ in relation to every other, 

 differ between themselves and also in comparison with the 

 blastoderm, from which they have originated. But the 

 diversity of the endoderm with respect to the ectoderm is 

 not of the same kind as its diversity in respect to the 

 blastoderm. n The potency of the endoderm and that of 

 the ectoderm are both specialised in their typical manner, 

 but compared with the potency of the blastoderm they 

 may be said not only to be specialised but also to be re- 

 stricted : the potency of the blastoderm embraces the whole, 

 that of the so-called germ-layer embraces only part of the 

 whole ; and this species of restriction becomes clearer and 

 clearer the further ontogeny advances : at the end of it in 

 the " ultimate elementary organs " there is no prospective 

 potency whatever. 



