IX] OF THE EADIOLARIAN SKELETON 711 



described; and that instead of forming a second hexagonal lattice- 

 work, the skeletal matter tends to be developed normally to the 

 surface of the sphere, that is to say along the radial edges where 

 the external vesicles (now compressed into hexagonal prisms) meet 

 one another three by three. The result will be that, if the vesicles 

 be removed, a series of radiating spicules will be left, directed 

 outwards from the angles of the original polyhedron mesh work, all 

 as is seen in Fig. 326. And it may further happen that thes6 

 radiating skeletal rods branch at their outer ends into divergent 

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



Fig. 326. Aulaatrum triceros Hkl. 



which we have already described as occurring in certain sponge- 

 spicules) to the superficial furrows between the three adjacent cells; 

 this is, as it were, a halfway stage between simple rods or radial 

 spicules and the full completion of another sphere of latticed 

 hexagons. Another possible case, among many, is when the large, 

 uniform vesicles of the outer protoplasm are replaced by smaller 

 vesicles, piled on one another in concentric layers. In this case 

 the radial rods will no longer be straight, but will be bent zig-zag, 

 with their angles in three vertical planes corresponding to the 

 alternate contacts of the successive layers of cells (Fig. 327). 



The solid skeleton is confined, in all these cases, to the boundary- 

 lines, or edges, or grooves between adjacent cells or vesicles, but 



