70 



not reproduced here. The form of Grovea pedalis (fig. 12) on the 

 contrary may be looked upon as an illustration of the group D, 

 whose representatives are very rare. Most of these figures were 

 reproduced after Haeckel's original drawings. 



Of the group D^ no instances have been found among the Dia- 

 tomeae] but perhaps some Radiolaries may belong to this class: so 

 Ethmosphaera siphonophora (Haeckel). If the top and the basal 

 parts of the fruit of Badamia Commersoni (fig. 73) were equally 

 developed, -- which is certainly not the case, this form would 

 give an idea of a vegetable object possessing this symmetry. 



Some pollen-cells, e. g. those of Passiflora augusti folia, Heliofropum 

 grandiflorum, etc., may be reckoned, according to some authors, 

 also to have this symmetry. 



The spicula of a number of Radiolaries are arranged in a regular and 

 most remarkable way. This special regularity was already described 

 by Joh. Miiller, and defined by him in a "rule" which bears his name. 

 The particular symmetry of this arrangement appears to be that of 



the group D^ ; as in the case of 

 Acanthostaums , Acanthometra, etc. 

 The pollen-cells of A nnona tripetala 

 also seem to belong here. 



A striking example of the symme- 

 try D^ in the C3.se oi Radiolaries, is 

 that of Acanthodesmia prismafium 

 (fig.$i), after Haeckel's drawing. 

 Haeckel was one of the first 

 to understand the eminent value 

 of the principle of symmetry for the 

 description of plants and animals, 

 and to draw special attention to the 

 symmetrical and highly aesthetic 

 forms of the lower beings, in his 



Acanthodesmia pnsmattum. _. 



great work on the Radiolaries, 

 and in his book: "Kunstformen der Natur". 

 This author 1 ) also made the first valuable attempts to found a 



*) E. Haeckel, Systematische Phylogenie; Entwurf eines natiirlichen Systems 

 der Organismen auf Grund ihrer Stammesgeschichte, End. / ///, Jena, (1894). 

 He speaks of four principal classes of forms: Centrostigma, Centroaxonia, Cen- 

 troplana, and Anaxonia. A comparison with our results must readily convince 

 everyone, that in his system a confusion of all classes is present. 



