IX] AND SPICULAR SKELETONS 467 



operation. If we perform the same experiment with oil and fine sand, 

 dropped into 70 per cent, alcohol, a still more beautiful artificial 

 Rhizopod shell is formed, but it takes some three hours to do. 



It is curious that, just at the very time when Rhumbler was 

 thus demonstrating the purely physical nature of the Difflu- 

 gian shell, Verworn was studying the same and kindred organisms 

 from the older standpoint of an incipient psychology*. But, as 

 Rhumbler himself admits, Verworn was very careful not to over- 

 estimate the apparent signs of volition, or selective choice, in the 

 little organism's use of the material of its dwelling. 



This long parenthesis has led us away, for the time being, 

 from the subject of the Radiolarian skeleton, and to that subject 

 we must now^ return. Leaving aside, then, the loose and scattered 

 spicules, which we have sufficiently discussed, the more perfect 

 Radiolarian skeletons consist of a continuous and regular structure ; 

 and the siliceous (or other inorganic) material of which this frame- 

 work is composed tends to be deposited in one or other of two 

 ways or in both combined: (1) in the form of long spicular axes, 

 usually conjoined at, or emanating from, the centre of the proto- 

 •plasmic body, and forming a symmetric radial system ; (2) in the 

 form of a crust, developed in various ways, either on the outer 

 surface of the organism or in relation to the various internal 

 surfaces which separate its concentric layers or its component 

 vesicles. Not unfrequently, this superficial skeleton comes to 

 constitute a spherical shell, or a system of concentric or otherwise 

 associated spheres. 



We have already learned that a great part of the body of the 

 Radiolarian, and especially that outer portion to which Haeckel 

 has given the name of the "calymma," is built up of a great mass 

 of "vesicles," forming a sort of stifE froth, and equivalent in the 

 physical sense (though not necessarily in the biological sense) to 

 "cells," inasmuch as the httle vesicles have their own well-defined 

 boundaries, and their own surface phenomena. In short, all that 

 we have said of cell-surfaces, and cell conformations, in our 

 discussion of cells and of tissues, will apply in hke manner, and 

 under appropriate conditions, to these. In certain cases, even in 



* Verworn, Psycho-physiologische Protlsten-Studien, Jena, 1889 (219 pp.). 



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