V] OF CERTAIN OSMOTIC PHENOMENA 275 



% concentration of salts in wkicli 



the sperm-cell of Inachus 



assumes the form of 



If we look then, upon the spherical form of the cell as its true 

 condition of symmetry and of equilibrium, we see that what we 

 call its normal appearance is just one of many intermediate phases 

 of shrinkage, brought about by the abstraction of fluid from its 

 interior as the result of an osmotic pressure greater outside than 

 inside the cell, and where the shrinkage of volume is not kept 

 pace with by a contraction of the surface-area. In the case of the 

 blood-corpuscle, the shrinkage is of no great amount, and the 

 resulting deformation is symmetrical ; such structural inequality 

 as may be necessary to account for it need be but small. But 

 in the case of the sperm-cells, we must have, and we actually do 

 find, a somewhat complicated arrangement of more or less rigid 

 or elastic structures in the wall of the cell, which like the wire 

 framework in Plateau's experiments, restrain and modify the 

 forces acting on the drop. In one form of Plateau's experiments, 

 instead of supporting his drop on rings or frames of wire, he laid 

 upon its surface one or more elastic coils; and then, on with- 

 drawing oil from the centre of his globule, he saw its uniform 

 shrinkage counteracted by the spiral springs, with the result that 

 the centre of each elastic coil seemed to shoot out into a prominence. 

 Just such spiral coils are figured 

 (after KoltzofE) in Fig. 96 ; and they 

 may be regarded as precisely akin to 

 those local thickenings, spiral and 

 other, to which we have already 

 ascribed the cylindrical form of the 

 Spirogyra cell. In all probabihty we 

 must in like manner attribute the 



peculiar spiral and other forms, for -p- nc o ' n j; r> 



^ ^ ' i< ig. 96. bperm-cell of Dromia. 



instance of many Infusoria, to the (After KoltzofE.) 



18—2 



