IX] 



OF THE RADIOLAKIAN SKELETON 



471 



regular and delicate, with the meshes just as beautifully hexagonal, 

 as in the siliceous shells of the oceanic Radiolaria. This is only 

 another proof (if proof be needed) that the peculiar conformation 

 of these little skeletons is not due to the material of which they 

 are composed, but to the moulding of that material upon an under- 

 lying vesicular structure. 



Let us next suppose that, upon some such lattice-work as has 

 just been described, another and external layer of cells or vesicles 

 is developed, and that instead of (or perhaps only in addition to) 

 a second hexagonal lattice-work, which might develop concen- 



Fig. 225. Aulastrum trlceros, Hkl. 



trically to the first in the boundary-furrows of this new layer of 

 cells, the siliceous matter now tends to be deposited radially, 

 or normally to the surface of the sphere, just in the lines where 

 the external layer of vesicles meet one another, three by three. 

 The result will be that, when the vesicles themselves are removed, 

 a series of radiating spicules will be revealed, directed outwards 

 from each of the angles of the original hexagon; as is seen 

 in Fig. 225. And it may further happen that these radiating 

 skeletal rods are continued at their distal ends into divergent 

 rays, forming a triple fork, and corresponding (after a fashion 



