726 ON CONCRETIONS, SPICULES, ETC. [ch. 



try to construct a plane-sided polyhedron of this kind, we find it 

 to be impossible; for into the angles between the six equatorial 



Fig. 340. Skeletons of various Radiolarians, after Haeckel. 1, Circoporus sexfurcus; 

 2, C. odahe.drus; 3, Circogonia icosahcdra; 4, Circospathis novena; 5, Circorrhegma 

 dodecahedra. 



regular hexagons six regular pentagons will not fit. The figure, 

 however, can be easily constructed if we replace the straight edges 



