EXPLANATION OF HYALINE APPEARANCE 265 



they exhibit he could establish the fact that the thickness of 

 the fluid lamella at the summit of a soap-bubble may sink 

 to O'OOOl mm. A lamella of such thinness nevertheless 

 exhibits great durability, since it maintains itself under 

 favourable circumstances for many days (Bd. ii. pp. 4, 5). 

 Hence there is theoretically nothing to oppose the notion 

 that the walls of the microscopic alveoli of protoplasm might 

 under certain circumstances become thinned out to invisi- 

 bility. To effect this a comparatively slight attenuation 

 would be quite sufficient, since when they are visible in the 

 living condition they are already so delicate and faint that, 

 if attenuated to a relatively small extent, they would dis- 

 appear from vision. 



This interpretation of the apparent homogeneity and 

 absence of structure in certain protoplasms is to a certain 

 degree strengthened by the observations that have already 

 been briefly described upon artificial froths. I pointed out 

 above that in a froth-drop sticking to the cover glass or slide, 

 the structure at the edges, where the drops spread out into a 

 perfectly flat thin layer, becomes so faint and indistinct that 

 it is at last no longer recognisable (p. 38 ; see Photographs 

 I. II.). The perfectly gradual diminution of distinctness 

 towards the edge, as well as slight traces of structure which 

 are still visible even in the apparently homogeneous edge, 

 prove that the nature of the edge is not really homogeneous, 

 but is also alveolar, and that the structure has merely 

 become too faint and delicate to show up distinctly any more. 

 I formerly tried to refer this phenomenon to the great 

 tenuity of the marginal border, and it is not without 

 importance in this respect that the homogeneous pseudo- 

 podia, as well as the homogeneous marginal layer of Rhizo- 

 pods, are mostly portions of the protoplasm which are very 

 thinly spread out upon the surface over which they are 

 creeping, although homogeneous protoplasm certainly occurs, 

 for which this statement does not hold good. 



In any case this discussion may serve to show that 

 the occasional transition of alveolar protoplasm into that 

 which is apparently quite homogeneous, is quite compatible 

 with the theory, and that on the ground of this fact no 



