THE LIVING SUBSTANCE. 



65 



ture of the living substance, lie partially, or wholly, concealed 

 optically others whose limits we cannot know and whose nature 

 is to be inferred to but a very small extent. 



By themselves, chemical differences constitute a mode of 

 areal differentiation of wide range within the limits of Butschli's 

 structure alone; and when the same holds true for the finer 

 structure it is evident that what we can resolve of internal vari- 

 ations in organization of the living substance is, indeed, but 

 a small part of all. That actual physical and physiological 

 differentiation of the living substance far outruns our power to 

 resolve local characters is certain. Hence optical differentiation 

 is not to be taken as the limit, or sum, of organization, or of the 

 physiological machinery of the living substance, but yet may be 

 taken as typical of this.^ 



[69] In so-called "low" and "primitive" forms of life, the 

 substance organization is seen to be very complex, if here as in 

 the Metazoa the sum of all areal differentiations be taken as 

 the unit of count ; but it is less stable and more fleeting, — 

 often, indeed, to the point of evanescence. Grosser structures 

 are openly transmuted, whereas in the adult higher forms there 

 is a more stable mask of structure behind which the substance 

 carries on its unstable processes. 



[70] Phylogeny is seen, from the standpoint of foam structure, 

 to be a direct progression along these lines in this direction, and 

 the types which follow each other in supposed evolutionary 

 sequence seem to typify the results in gross of such progression. 



[71] In all forms, from the lowest to the highest examined — 

 subtly hidden often, it is true, beneath the stable as well as be- 

 neath the openly unstable structures — exist fleeting differentia- 

 tions. Nowhere, unless secondarily modified so as to lose its 

 vital state, is found a protoplasmic structure so stable and fixed 

 as regards the substance as such that it does not permit these ; 

 nor does such stability of structure involve or imply renuncia- 

 tion of the instability of the substance as such.^ Take, for 

 instance, such very stably organized areas as the contractile 

 cuticle of Epistylis, or the delicate skin of the rotifer, or muscle 



1 See next section, Activities. 



2 See pellicles and alveolar layers, above; and next section, on Activities. 



