1 8 ANDREWS. 



cellulose wall of Spirogyra, then, exists at first as a sub- 

 stance inclusion.^ 



Throughout the series of structural subdivisions of proto- 

 plasm the inclusions are for the most part unstable. They are 

 seen to increase either slowly or rapidly by purely physical 

 changes ; and they suffer change also by what must still be 

 called physiological activities of the interalveolar protoplasm. 

 They grow by absorption of material from, or through, the sur- 

 rounding substance ; they wane by diffusion in the same mode ; 

 they are at times suddenly augmented by relaxed states of the 

 nearest interalveolar stuff, or of the whole area, or mass, and may 

 then attain such size as to rank with " vacuolations " ; or, from 

 a size too small to be directly seen as alveoli, may be brought 

 into the range of the structure of Butschli. 



Inclusions may be also more or less rapidly increased in size 

 by withdrawal of the interalveolar substance, which involves, 

 or leads to bursting of, the lamellae ; throwing together the 

 contents of adjoining alveoli. Besides a purely physical cause 

 of this sort, such as is familiar in soap-foams, there are cases 

 in which the interalveolar, if not the lamellar, substance craiuls 

 or flows away from between alveoli. This phenomenon has 

 been seen in many Protozoa ; typical instances are readily 

 watched in Heliozoa, as Actinosphaerium. In the formation by 

 these of tubular rays, and by Acinetans of hollow tubes or suc- 

 torial tentacles, there can be little doubt as to the way in which 

 the transfer of protoplasm takes place.^ 



In Acinetans there is formed a rod-like extension of the 

 substance, which by successive redistributions of the elements 

 becomes at last a mere row of alveoli of about equal size. The 

 network of the whole has the effect of a "ladder," whose 

 sides are increasingly thickened by immigration of protoplasm 

 from the "rounds." These latter are finally obliterated as a 

 result of this, and the whole interior is then one long closed 



1 It is not impossible that to contractions of such a film of organized proto- 

 plasm may be due the movements of many plant filaments, as Oscillatoria, etc. 

 See Striation. 



2 Each one of these phenomena, it must be remembered, can be fully grasped 

 only by aid of all the facts given in this paper, which are supported by hundreds 

 not given. For above, see also Activities of the Continuous Substance. 



