XII] OF THE FORAMINIFERA 863 



assuming that the protoplasm has a different composition and 

 different properties (including a very different distribution of 

 surface-energy), at points near to and remote from the mouth of 

 the shell. Whether the. differences in angle of contact be as great 

 as Rhumbler takes them to be, whether marked heterogeneities of 

 the protoplasm occur, and whether these be enough to account for 

 the differences of angle, I cannot tell. But it seems to me that 

 we had better rest content with a general statement, and that 

 Rhumbler has taken too precise and narrow a view. 



Fig. 429. Cristellaria reniformis d'Orb 



In the molecular growth of a crystal, although we must of 

 necessity assume that each molecule settles down in a position of 

 minimum potential energy, we find it very hard indeed to explain 

 precisely, even in simple cases and after all the labours of modern 

 crystallographers, why this or that position is actually a place of 

 minimum potential. In the case of our httle Foraminifer (just as 

 in the case of the crystal), let us then be content to assert that each 

 drop or bead of protoplasm takes up a position of minimum potential 

 energy, in relation to all the circumstances of the case ; and let us 

 not attempt, in the present state of our knowledge, to define that 

 position of minimum potential by reference to angle of contact or 

 any other particular condition of equilibrium. In most cases the 

 whole exposed surface, on some portion of which the drop must 

 come to rest, is an extremely complicated one, and the forces in- 

 volved constitute a system which, in its entirety, is more complicated 



