IX] OF THE RADIOLARIAN SKELETON 723 



between; so far so good, again. But the irregular lacework of the 

 Uttle helmets does not suit this explanation very well, and there 

 may be yet other possibilities. We have already mentioned 

 Tomhnson's "cohesion figures*." Experimenting with a great 

 variety of substances, Tomhnson studied the innumerable ways in 

 which drops, jets or floating films "cohere," disrupt or otherwise 

 behave, under the resultant influences of surface-tension, cohesion, 

 viscosity and friction; in one case a film runs out into a wavy or 

 broken edge, in another it gives way here and there, and makes 

 rents or holes in its surface. I take the Httle holes in our poly cystine 

 skeleton to be cohesion-figures, in Tomhnson's sense of the word — 

 spots where the delicate film has given way and run into holes, and 

 where surface-tension has rounded off the broken edges, and made 

 the rents into rounded apertures. 



In the foregoing examples of Radiolaria, the symmetry which 

 the organism displays seems identical with that symmetry of forces 

 which results from the play and interplay of surface-tensions in the 

 whole system : this symmetry being displayed, in one class of cases, 

 in a more or less spherical mass of froth, and in another class in 

 a simpler aggregation of a few, otherwise isolated, vesicles. In 

 either case skeletons are formed, in great variety, by one and the 

 same kind of surface-action, namely by the adsorptive deposition 

 of sihca in walls and edges, corresponding to the manifold surfaces 

 and interfaces of the system. But among the vast number of 

 known Radiolaria, there are certain forms (especially among the 

 Phaeodaria and Acantharia) which display a no less remarkable 

 symmetry the origin of which is by no means clear, though surface- 

 tension may play a part in its causation. Even this is doubtful; 

 for the fact that three-way nodes are no longer to be seen at the 

 junctions of the cells suggests that another law than that of minimal 

 areas had been in action here. They are cases in which (as in some 

 of those already described) the skeleton consists (1) of radiating 

 spicular rods, definite in number and position, and (2) of inter- 

 connecting rods or plates, tangential to the more or less spherical 

 body of the organism, whose form becomes, accordingly, that of a 

 geometric, polyhedral sohd. The great regularity, the numerical 



♦ Cf. supra, p. 418 



