8 ANDREWS. 



a whole, very viscid, resistant to pressure, elastic, and even 

 contractile. 1 



The " shagreen " appearance above referred to, when caused 

 by Biitschli's structure, is best seen in peripheral areas, espe- 

 cially where there is a marked alveolar layer ; but whether this 

 latter be present or not, the shagreen effect can be strongly 

 marked. It is always to be made out also (if there be no 

 optical interference of substances), where alveoli, many or few, 

 lie in the same plane, or nearly so. The blistered appearance 

 may not come to the surface of pellicles, but lie more or less 

 deep within these which vary greatly in thickness ; and the 

 actual pellicular surface may be covered more or less unstably 

 by a far finer shagreen, whose alveoli will measure only from 

 one-sixth to one-twelfth /i^. 



Alveolar blistering, whether of the finer froth, or of Biitschli's 

 structure, does not always roughen the actual surface, but may 

 be much flattened ; and further, may be covered by a secondary 

 pellicular film ; or in other cases may project so as to cause an 

 optical roughening of the surface when seen from the side. 

 I have not, however, in any case yet seen, been able to assure 

 myself that the actual surface of any pellicular shagreen, how- 

 ever delicate, as seen from above, was not covered by yet 

 another pellicle. 



The smooth expanse of protoplasm found everywhere above 

 and below networks and alveolar contours proves even more 

 conclusively than does the network itself, the presence between 

 inclusions of a lamellar substance. In even swiftly flowing and 

 unstable areas it can be seen forming structureless, or blank, 

 surfaces, which break into fragments the network image, as the 

 flux of the substance carries this above or below focus. The 

 blank spaces are in their turn broken by rounded contours of 

 alveoli rising or falling into focus, and then by reappearance 

 of clearly marked network images.^ 



1 See Continuous Substance ; Activities — filose. 



2 See p. 9- 



8 One may with practice follow for many moments at a time the course of small 

 groups of alveoli, or even of one or two, in the endosarc of amoebae and other Pro- 

 tozoans, and in the early stages of the development of the starfish and echinus 

 eggs ; and while doing so, the true nature of these expanses of " shagreen " texture, 



