METHODS OF PHYSIOLOGICAL ANALYSIS 85 



within its developing system. As far as relations to other parts are con- 

 cerned, a reconstituting hydroid or planarian piece is undergoing self-de- 

 velopment; but within the piece reconstitution depends on an orderly and 

 definite pattern of relations, on dominance of certain parts and subordina- 

 tion of others. Self-differentiation or self-development occurs only when a 

 pattern already present persists in the part after its isolation or transplan- 

 tation. Such a part is said to be "determined," that is, its pattern is re- 

 garded as fixed. Labile and definitive determination are often distin- 

 guished. It cannot be too strongly emphasized, however, that determina- 

 tion is always relative to a particular environment or environments. To 

 conclude that a pattern is unalterable because it is not altered by isolation 

 or by transplantation is entirely unjustified. There is always the possibil- 

 ity that in some other environment it may undergo alteration. In fact, this 

 occurs in some transplantation experiments; the pattern of a part trans- 

 planted to a certain region of a host may persist, but with transplantation 

 to another region it may undergo alteration. Undoubtedly, progressive 

 stabilization or fixation of pattern or the basis of differentiation does occur 

 in the course of development, even before pattern or differentiation be- 

 come visible. Determination, in the sense of a more or less stable disposi- 

 tion or tendency to develop in a certain way before that development be- 

 comes evident, obviously represents a change from an earher undeter- 

 mined condition. Isolation or transplantation may give evidence of it but 

 tells us nothing concerning its nature. To say that a part is determined 

 means only that it possesses a certain disposition as regards further activ- 

 ities and involves no implications concerning the nature of that disposi- 

 tion. If we keep in mind the possibility that even the most obstinate dis- 

 positions may not be unalterable and that the word "determination" is an 

 expression of our ignorance, it serves a useful purpose. 



