600 



THE SPIRAL SHELLS 



[CH. 



but little is known, save only in the particular case where one of 

 the three bodies is air, as when a surface of water is exposed to 

 air and in contact with glass. It is easy moreover to see that in 

 many of our Eoraminifera the angle of contact, though it may be 

 constant in homologous positions from chamber to chamber, is 

 by no means constant at all points along the boundary of each 

 chamber. In Cristellaria, for instance (Fig. 315), it would seem 

 to be (and Rhumbler asserts that it actually is) about 90° on the 

 outer side and only about 50° on the inner side of each septal 

 partition ; in Pulvinuhna (Fig. 259), according to Rhumbler, the 

 angles adjacent to the mouth are of 90°, and the opposite angles 



Fig. 315. Cristellaria ^reniform is, d'Orb. 



are of 60°, in each chamber. For these and other similar discre- 

 pancies Rhumbler would account by simply invoking the hetero- 

 geneity of the protoplasmic drop : that is to say, by 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. 



