42 



ANDREWS. 



physiological activity, there was found also physical organiza- 

 tion of the two groups of elements of Biitschli's, or a finer, 

 or a coarser, foam structure, with or without further physical 

 modification of the given interalveolar structure. As to the 

 observer's perception, this organization arises sometimes simul- 

 taneously with the activity, sometimes precedes it, and may 

 outlast it, but always accompanies it. 



(a) It does not necessarily follow that the structure visible 

 to the observer in a physiological area is that which is to be 

 correlated with the given function ; nevertheless it is true, 

 as will be shown, that function and vesicular structure are 

 indeed too closely linked for us now to set them apart. 



(b) Capricious as seems the substance, unstable and incal- 

 culable as are its manifestations, there can yet be found certain 

 broad laws, or rather habits, of structural arrangement under 

 which it is wont to express itself. 



(c) Under the head of pellicles somewhat was indicated of 

 the manner in which masses of protoplasm are subdivided and 

 differentiated structurally by arrangement of the continuous 

 substance and the inclusions, and by the character of these two 

 sets of elements. And to pellicular formation much of the 

 optical, as well as physical and physiological, differentiation of 

 areas is due. (See also Ectosarc.) 



The majority of facts relating to these things are so inextri- 

 cably correlated with phenomena of the substance as such, 

 which must be grouped under the head of activities, that they 

 will be treated of in that section, but some few important gen- 

 eralizations are offered here. 



[40] Two groups of areal differentiation are most marked, 

 — those in which the function is of a vegetative sort, and those 

 in which it is organized or emphasized irritable or contractile 

 function, or both. 



In the former case the continuous substance has not usually 

 that marked refractive and viscous emphasis, stable or rhythmic, 

 which peculiarly characterizes the other group of structures, 

 yet such there may be, at intervals during active secretion, as 

 was seen in the gland of a certain rotifer {MegalotrocJia), 

 which, situated by the point of exit, pours out a glairy sub- 



