154 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



type of " systems " which play a part in morphogenesis ; a 

 type which we have shortly mentioned already and which 

 will be studied fully a few chapters later. We know that 

 there are equipotential systems with complex potencies : that 

 is to say, systems which may produce a whole organism 

 equally well from any one of their elements ; we know the 

 cambium of Phanerogams to be such a system. Now it is 

 easily understood that the germ of our Echinus, say in the 

 stage of two or four or eight cleavage cells, is not only an 

 harmonious-equipotential system, but a cornplex-equipotential 

 system too. Not only may there arise a whole organism 

 out of J or j or -|, ^, -|, |, -- of its elements, in which cases 

 the harmonious role of the single element with regard to 

 its single performance in a totality is variable, but there 

 may also arise four whole single larvae out of the four cells 

 of the four-cell stage, or eight single whole larvae out of the 

 eight-cell stage. 1 In these cases, of course, each of the 

 four or eight elements has performed not a part of the 

 totality, changing with its "position," but the totality 

 itself. With respect to these possible performances the 

 " systems " present in the four or eight-cell stages of cleavage 

 must be called complex-equipotential ones. 



We propose to give the name of mixed-equipotential 

 systems to all those equipotential systems which, at the 

 same time, may be regarded as belonging to the harmonious 

 or to the complex type. It is not only among cleavage- 

 stages that they are to be found ; you may also find them 

 very clearly exhibited in our ascidian Clavellina for instance. 



1 The eight larvae would be incomplete in some respect, but not with 

 regard to symmetry. They would be "whole" ones, only showing certain 

 defects in their organisation. See page 65 note 1, and page 73. 



