84 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



A few new terms will serve to state a little more 

 accurately what happens. Of course, with regard to all 

 morphogenesis which goes on immediately from the blasto- 

 derm, the potency of the blastoderm is restricted as much 

 as are the potencies of the germ layers. We shall call this 

 sort of immediate potency explicit, and then we see at once 

 that, with regard to their explicit potencies, there are only 

 differences among the prospective potencies of the elementary 

 organs ; but with respect to the implicit potency of any of 

 these organs, that is with respect to their potency as em- 

 bracing the faculties of all their derivations, there are also 

 not only differences but true morphogenetic restrictions 

 lying at the very foundations of all embryology. 



But now those of you who are familiar with morpho- 

 genetic facts will object to me, that what we have stated 

 about all sorts of restrictions in ontogeny is not true, and 

 you will censure me for having overlooked regeneration, 

 adventitious budding, and so on. To some extent the 

 criticism would be right, but I am not going to recant ; 

 I shall only introduce another new concept. We are 

 dealing only with primary potencies in our present con- 

 siderations, i.e. with potencies which lie at the root of true 

 embryology, not with those serving to regulate disturbances 

 of the organisation. It is true, we have in some way 

 disturbed the development of our sea-urchin's egg in 

 order to study it; more than that, it would have been 

 impossible to study it at all without some sort of disturb- 

 ance, without some sort of operation. But, nevertheless, 

 no potencies of what may properly be called the secondary 

 or restitutive type have been aroused by our operations ; 

 nothing happened except on the usual lines of organogenesis. 



