V] 



OF CEETAIN OSMOTIC PHENOMENA 



273 



of the surface may itself modify the osmotic or perhaps the adsorp- 

 tive action. If it should be found that osmotic action tended to 

 stop, or to reverse, on change of curvature, it would follow that 

 this phenomenon would give rise to internal currents ; and the 

 change of pressure consequent on these would tend to intensify 

 the change of curvature when once started*. 



The sperm-cells of the Decapod Crustacea exhibit various 

 singular shapes. In the Crayfish they are flattened cells with 

 stiff curved processes radiating outwards like a St Catherine's 

 wheel ; in Inachus there are two such circles of stif? processes ; 

 in Galathea we have a still more complex form, with long and 



Fig. 94. Sperm-cells of Decapod Crustacea (after Koltzoff). a, Inachus scorpio; 

 b, Galathea squamifera ; c, do. after maceration, to shew spiral fibrillae. 



slightly twisted processes. In all these cases, just as in the case 

 of the blood-corpuscle, the structure alters, and finally loses, its 

 characteristic form when the nature or constitution (or as we may 

 assum.e in particular — the density) of the surrounding medium is 

 changed. 



Here again, as in the blood-corpuscle, we have to do with a 

 very important force, which we had not hitherto considered in this 

 connection, — the force of osmosis, manifested under conditions 

 similar to those of Pfeffer's classical experiments on the plant-cell. 

 The surface of the cell acts as a "semi-permeable membrane," 



* For an attempt to explain the form of a blood-corpuscle by surface-tension 

 alone, see Rice, Phil. Mag. Nov. 1914; but cf. Shorter, ibid. Jan. 1915. 



T. G. 18 



