68 ANDREWS. 



mic mass ; there is thus given no true assurance that the living 

 substance is at rest. Mass pellicles, alveolar layers, and, within 

 these, area upon area of structural differentiation, may lie seem- 

 ingly unchanged from minute to minute, or from day to day, or 

 even throughout the rest of the lifetime of an organism, after 

 they are once formed; and still a continuous train of substance 

 activities go on, resulting in formation of new structures, both 

 within and without the mass. 



The coexistence of a stable and perfect structure of Biitschli 

 with a host of metamorphosing activities of the substance as 

 such ; this forms one of the strongest reasons I would urge for 

 preferring optical research upon living material to more indirect 

 methods. 



\y6\ The continuous substance of Biitschli's structure seems 

 to be very active in all organisms observed. It is indeed most 

 commonly in a state of flux, or of active contraction. Some- 

 times the two states are found to exist interchangeably in the 

 same area which may be stably organized, even for contractile 

 purposes, as in the cuticle of Vorticellidae, or the delicate skin 

 of rotifers. In pellicles, whether internal or external, excepting 

 those which have been wholly altered by deposit of mineral 

 substance, or chitin, or the like; no matter how stable and per- 

 sistent their seeming under inadequate powers, no matter how 

 stable as such the structure of Biitschli underlying them; there 

 are evidences at one time or another, or at most times, of a 

 more or less active flux, or of contractile displacement. Areal, 

 or mass, viscosity so great as to produce considerable resistance 

 to mechanical tension or pressure, seems no bar to unrest of 

 the continuous substance. 



(a) Alveolar layers and many other areal organizations of the 

 substance are constantly intermitted, or broken up, by such 

 instability of the continuous substance, which is comprehensible 

 only through knowledge of its finer foam structure. In the 

 finer structure itself is again repeated the same set of phenom- 

 ena,^ so that it is plain we cannot stop even here satisfied with 

 foam structure as an adequate explanation. 



(b) The motion of the "granules" upon the surface of very 



^ See filose phenomena, cilia, etc., below. 



