EXPERIMENTAL MORPHOGENESIS 79 



We consequently may shortly formulate our first problem 

 as the question of the distribution of the prospective 

 morphogenetic potencies in the germ. Now this general 

 question involves a number of particular ones. Up to what 

 stage, if at all, is there an absolutely equal distribution of 

 the potencies over all the elements of the germ ? When 

 such an equal distribution has ceased to exist at a certain 

 stage, what are then the relations between the parts of 

 different potency ? How, on the other hand, does a newly 

 arisen, more specialised sort of potency behave with regard 

 to the original general potency, and what about the distribu- 

 tion of the more restricted potency ? 



I know very well that all such questions will seem to 

 you a little formal, and, so to say, academical at the outset. 

 We shall not fail to attach to them very concrete meanings. 



The Potencies of the Blastomeres 



At first we turn back to our experiments on the egg of 

 the sea-urchin as a type of the germ in the very earliest 

 stages. We know already that each of the first two, or each 

 of the first four, or three of the first four blastomeres together 

 may produce a whole organism. We may add that the 

 swimming blastula, consisting of about one thousand cells, 

 when cut in two quite at random, in a plane coincident with, 

 or at least passing near, its polar axis, may form two fully 

 developed organisms out of its halves. 1 We may formulate 

 this result in the words : the prospective potency of the 



1 If the plane of section passes near the equator of the germ, two whole 

 larvae may be formed also, but in the majority of cases the "animal" half 

 does not go beyond the blastula. The specific features of the organisation 

 of the protoplasm come into account here. See also page 65, note 1. 



