40 ANDREWS. 



delicate to avoid gross vacuolation of the structure of Biitschli, 

 alveolar layers are marked. 



The fact that in the living substance these layers are less 

 stably present than Biitschli supposed does not militate against 

 his theory of the structure of protoplasm. It is, on the con- 

 trary, enforced, because the moment the substance as such 

 is released from certain physiological controls, it proves its 

 physical form by acting as a mere visco-fluid foam. 



[35] While I find alveolar layers to be expressive of the 

 physical form of the protoplasmic foam, they are not neces- 

 sarily due to this alone, but may express also effects of physio- 

 logical states and physiological activities. 



Many alveolar layers given by preservation methods express an 

 osmotic vacuolation of the living structure. This can be proven 

 by use of reagents on living material under the microscope. 



[36] Contrary to all the conditions found necessary by 

 Biitschli for alveolar layers in artificial foams, I find the living 

 substance forming freely, in a moment, at any point in its mass, 

 and while the general structure of Biitschli is of markedly 

 irregular size, and the mass or area is of marked viscosity ; 

 perfect alveolar layers. 



The most interesting instance I know of this is afforded by 

 the formation in developing echinus eggs of a perfect and 

 double alveolar layer internally to the cell-mass. This after- 

 wards becomes for a short time part of the external peripheral 

 layer of the new cells, the split taking place between the two 

 rows of vesicles. 



[37] Marked viscidity of a mass, or area, of protoplasm 

 seems no bar to formation of a very perfect alveolar layer ; the 

 irregularity of its existing structure, no impediment ; nor, on 

 the other hand, is the fluidity of a living area or mass any 

 guarantee that there we shall find a definite alveolar layer, 

 except more or less unstably. The living foam, then, is able 

 in this respect to defy, or set aside, those controls which rule 

 the purely artificial foams of Biitschli. 



In artificial foams the finer vesicles tend to range themselves 

 peripherally to the mass, the outermost layer, in foams which 

 are not very viscid, being the alveolar layer. 



