36 



Fig. 26. 

 Fruit of 



Helicteres baruensis. 



and in fig. 25 a part of a Medusa: Aurelia insulinda (Haeckel), 

 seen from below, and showing 

 the symmetry of group C 4 . 



Most remarkable in this 

 respect is the egg-cleavage of 

 the hemimorphic cells in the 

 parthenogonidium of Volvox 

 globator l ), which originally 

 shows the symmetry C V 4 , but 

 which already in the second 

 stage changes to C 4 , and thus 

 remains till the end. The 

 structure of these individuals 

 rotating to the right, is dex- 

 trogyratory, and doubtless 

 there must be a relation 

 between both phenomena. It 

 were of interest to find a laevogyratory speci- 



CMamydia tenadssima. men of this interesting protist, which therefore 

 probably at the same time would appear to 



rotate in an opposite direction 



during its motion. 



As further instances the blossom- 

 diagrams of Triphasia trijoliata(C 3 ), 



of Polemonium coeruleum (C 5 ), of 



Hydrophyllum virginianum (C 5 ) , and 



perhaps of Roxburghia gloriosoides 



(C 2 ), might be mentioned. 



If n = 1 , the stereometrical figure 



has no symmetry at all; thus all 



asymmetric objects belong to this 



group Q. As examples of natural 



objects of this kind, we may mention 



the blossoms of Canna Sellowiana, 



Fig. 25. 



Fruit of 



Fig. 27. 



Auvelia insulinda. 



quadrifolia, whose quaternary symmetry is present both in the blossom and in 

 the phyllotaxis of the plant (Cf. : J. Sachs, Vorlesungen iiber Pflanzen-physiologie, 

 p. 600, Fig. 331), is a rare exception to this rule. On the other hand, the 

 five-fold symmetry seems to be most general for Dicotyledons; sometimes also 

 the four-fold symmetry appears to be of importance in this case. 



!) H. C. Delsman, Proceed. Kon. Acad. v. Wet. Amsterdam, 21. 243. (1918). 



