6 Elementary Zoology 



fluid parts; in this case the granules are largely an optical 

 delusion, and represent the nodal points of the meshwork : the 

 granules are also partly "formed" substances, i.e. bodies not 

 protoplasm, but produced by the activity of the protoplasm, 

 just as the droplets of fat in a fat cell are formed substances 

 produced by the activity of the protoplasm. A mass of proto- 

 plasm, then, on this view, may be roughly compared to a sponge. 



Fig. 2, — A portion of the body of a Multinucleate infuKorian Opalina, to show 

 network structure of protoplasm. Very highly magnified. (After Eiitschli.) 



According to the foam or honeycomb theory the living 

 substance of a cell is comparable to a mass of froth, of which 

 the air in the bubbles is formed by less viscid, the walls of the 

 bubbles by more viscid, protoplasm. It will be apparent that 

 so far this view of the constitution of protoplasm does not differ 

 widely from the network view. The protoplasm of various 

 cells and certain simple organisms appears to demonstrate that 

 this foam theory is the true explanation of the arrangement of 

 protoplasm. It is especially well seen in an amoeboid creature 



