716 ON CONCRETIONS, SPICULES, ETC. [ch. 



equilateral triangular prism; and Haeckel's Prismatium tripodium 

 repeats this configuration (Fig. 332). 



In a framework of two crossed rectangles, we may insert one 

 bubble after another, producing a chain of superposed vesicles whose 

 shapes vary as we alter the relative positions of the rectangular 

 frames. Various species of Triolampas, Theocyrtis, etc. are more 

 or less akin to these complicated figures of equilibrium. A very 

 beautiful series of forms may be made by introducing successive 

 bubbles within the film-system formed by a tetrahedron or a 



Fig. 332. Prismatium tripodium Hkl. 



parallelepipedon. The shape and the curvature of the bubbles 

 and of their suspensory films become extremely beautiful, and we 

 have certain of them reproduced unmistakably in various Nassel- 

 larian genera, such as Podocyrtis and its allies. 



In Fig. 333 we see a curious little skeletal structure or complex 

 spicule, whose conformation is easily accounted for. Isolated spicules 

 such as this form the skeleton in the genus Dictyocha, and occur 

 scattered over the spherical surface of the organism (Fig. 334). The 

 basket-shaped spicule has evidently been developed about a cluster 

 of four cells or vesicles, lying in or on the surface of the organism, 

 and therefore arranged, not in the three-dimensional, tetrahedral 

 form of Callimitra, but in the manner in which four contiguous cells 

 lying side by side in one plane normally set themselves, like the 



