DEVELOPMENTAL MECHANICS. I 65 



admission of energy from without, in the form of heat, oxygen, 

 etc., is necessary. In order to distinguish the two cases the 

 term "complete self-differentiation" was employed when 

 all the components lie within the formed part itself, while 

 "incomplete self-differentiation" obtains when the acces- 

 sion of energy from without is required, in so far as this 

 energy represents only the preexisting condition of the forma- 

 tive operation in the sense above accepted; but since, never- 

 theless, the accession of energy from without in the form of 

 heat, light, gaseous, and liquid nutriment, is in varying quan- 

 tity necessary to the development of the eggs of different ani- 

 mals, but does not determine whether an egg is to develop into 

 a chick, a frog, or a fish, or whether the lung is to be laid down 

 at a particular spot in the embryo, the development of the egg 

 would be more accurately designated as " incomplete self-differ- 

 entiation." 



As was set forth above, self-differentiation in the strict 

 dynamical and analytical sense, can, of course, have no exist- 

 ence, since every change in a phenomenon must depend on 

 reciprocal operations. Since the concept "self-differentia- 

 tion " is, accordingly, not processual but merely topographical, 

 implying something with regard to the locality of the causes 

 of the formative process, whenever it is employed, the particu- 

 lar circumscribed structure to which it refers must be men- 

 tioned. 



" Dependent differentiation " is a change in which one or 

 more of the components that condition the specific formation, 

 operate from without on the circumscribed or presumably cir- 

 cumscribed part to be formed ; and " passive differentia- 

 tion " occurs when all of the components of the respective 

 formative process of a given part operate from without, as, e.g., 

 in the modeling of a figure in clay or wax. 



Self-differentiation and dependejit differentiation may occnr 

 in the most varied combination either simultaneously or succes- 

 sively. 



Thus the normal formation of skeletal structures like the tibia 

 is very probably partially due to self-differentiation, because, 

 presumably apart from external influences, there arises from 



