Xos. 022-623] ORGANIC EVOLUTION 



541 



that the development of the striae has in many forms pro- 

 ceeded so far that a reversal rotation seems an impossi- 

 bility. 



The presence of a considerable number of other groups 

 which have "left-handed" spirals so far as observation 

 goes, is of interest. The various genera of Spirochetes, 

 as well as Spirulina and Arthrospira among the Cyano- 



phycoidea (Cymophycea) may be mentioned. The 

 twining of plants may, in the final analysis, be attrib- 

 utable to the same cause. 



Other related problems are the pendulation theory of 

 Simroth (1912) relative to bipolar distribution, and the 

 tropism theory as outlined by Verworn (1894), in con- 

 nection with the excitation contraction of the flagellum. 



