XII] OF THE FORAMINIFERA 853 



elements of the shell-wall. But the calcareous needles are secreted 

 in, or by, no less long and dehcate pseudopodia or "filopodia," 

 and much has been learned since this book was written of the 

 molecular, or micellar, orientation of the protoplasm in such 

 filamentous structures; it is known that the long pseudopodia of 

 the Foraminifera are doubly refractive, and it follows that their 

 molecules are anisotropically arranged*. Whether the slender form 

 and asymmetrical structure of calcareous rod and protoplasmic 

 thread be independent phenomena, or merely two aspects of one 

 and the same phenomenon, is a hard question, and not one for us 

 to discuss. Nor can we profitably discuss (much as we should like 

 to know) how far these patterns of molecular structure in threads, 

 films and surface-pelHcles aifect the "fluidity" of the substance, 

 and conflict with the capillary ' forces which influence its outward 

 form. But we may safely say that the effects of surface-tension 

 on cell-form have been so plainly seen all through this book that 

 any counter-effects due to protoplasmic asymmetry must be 

 phenomena of a second order, and inconspicuous on the whole. 

 Over the whole surface of the shell of Globigerina the radiating 

 spicules tend to occur in a hexagonal pattern, symmetrically 

 grouped around the pores which perforate the shell. Rhumbler 

 has suggested that this arrangement is due to diffusion-currents, 

 forming little eddies about the base of the pseudopodia issuing from 

 the pores: the idea being borrowed from Benard, to whom is Hue 

 the discovery of this type or order of vortices f. In one of Benard's 

 experiments a thin layer of parafiin is strewn with particles of 

 graphite, then warmed to melting, whereupon each little sohd granule 

 becomes the centre of a vortex ; by the interaction of these vortices 

 the particles tend to be repelled to equal distances from one another, 

 and in the end they are found to be arranged in a hexagonal pattern J. 



* Cf. W. J. Schmidt, Die Bausteine des Tierkorpers in polarisiertem Lichte, 

 Bonn, 1924; Ueber den Feinbau der Filopodien; insb. ihre Doppelbrechung bei 

 Miliola, Protoplasma, xxvii, p. 587, 1937; also D. L. Mackinnon, Optical pro- 

 perties of contractile organs in Heliozoa, Jl. Physiol, xxxviii, p. 254, 1909; 

 R. 0. Herzog, Lineare u. laminHre Feinstrukturen, Kolloidzschr. lxi, p. 280, 1932. 

 See, for discussion and bibliography, L. E. Picken, op. cit. 



t H. Benard, Les tourbillons cellulaires, Ann. de Chimie (8), xxiv, 1901. Cf. 

 also the pattern of- cilia on an Infusorian, as figured by Biitschli in Bronn's 

 Protozoa, iii, p. 1281, 1887. 



X A similar hexagonal pattern is obtained by the mutual repulsion of floating 

 magnets in Mr R. W. Wood's experiments, Phil. Mag. xlvi, pp. 162-164, 1898. 



