108 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



that is to say, in lines of processes which may start from a 

 common root, but which are absolutely independent of 

 one another in their manner of differentiation. Eoux has 

 coined the term " self-differentiation " to denote this pheno- 

 menon, and we admit that this term may be conveniently 

 used for the purpose, if only it can be kept in mind that 

 its sense is always relative, and that it is also negative. 

 Suppose a part, A, shows the phenomenon of self-differ- 

 entiation : this means that the further development of A 

 is not dependent on certain other parts, B, C, and D ; it does 

 not mean at all that A has not been formatively dependent 

 on some other parts, E or F at the time of its first appear- 

 ance, nor does it imply that there might not be many 

 formative actions among the constituents of A itself. 



We indeed are entitled to say that the ectoderm of 

 Echinus shows " self-differentiation ' with regard to the 

 endoderm ; it acquires its mouth, for instance, as has been 

 shown by experiment, even in cases where no intestine is 

 present at all (Fig. 10); but ectoderm and endoderm both 

 are formatively dependent on the intimate and the material 

 organisation of the blastoderm. It further seems from the 

 most recent experiments that the nerves and the muscles of 

 the vertebrates are independent of each other in their 

 differentiation, but that their fate is probably determined 

 by formative processes in the very earliest stages of ontogeny. 



The phenomenon of self- differentiation, properly under- 

 stood, now may help to the discovery of one most general 

 character of all development. If the phenomenon of self- 

 differentiation really occurs in ontogeny in its most different 

 aspects, and if, on the other hand, in spite of this relative 

 morphogenetic independence of embryonic parts, the result- 



