46 



needs no detailed discussion to see, that every figure of this kind may 



also exist in a second form which is the mirror-image of the other one. 



In the domain of living objects, a number of highly remarkable 



Fig. 48. 



Circoporus octahedrus. 



Fig. 49. 

 Circorhegma dodecahedra. 



instances of all three groups T, K, and P are known. Indeed, there is 

 nothing to prevent the occurrence of the symmetry of group P in living 

 nature, as there is in the case of crystalline matter. On the contrary, 

 it seems that living objects show a certain preference for symmetry- 

 axes of a period of . 



. As interesting examples of this 

 kind, we may mention the splen- 

 did forms of some Radiolaries 

 (Phaeodaria) : of Circoporus octa- 

 hedrus (fig. </<?), of Circorhegma 

 dodecahedra (fig. 49), and of 

 Circogonia icosahedra (fig. 50), 

 all according to Haeckel's origi- 

 nal descriptions. They are very 

 striking instances of the sym- 

 metry of the groups K and P 

 respectively, and these animals 

 manifest in a most convincing 

 way their morphological relations to the regular endospherical 

 polyhedra, and more especially to the octahedron, the pentagonal 

 dodecahedron, and the icosahedron. 



Fig. 50. 



Circogonia icosahedra. 



