Nos. 622-623] ORGANIC EVOLUTION 



531 



which within certain limits allows a plasticity in the de- 

 velopment, and that the direction of development is de- 

 termined by physico-chemical influences through the 

 suppression of potential units. 



Thus the conclusion seems almost unavoidable that by 

 far the larger number, if not all, of the heritable charac- 

 ters making up an organism, result from combinational 

 units which have long been predetermined, and that the 

 breeder, whether the semi-scientific agriculturist or the 

 ultra-scientific drosophilist, is largely, if not entirely, en- 

 gaged in presenting new combinations of existing units. 

 If this be true, modern genetics has left the actual prob- 

 lem of evolution far to one side and deals only with re- 

 sults of a secondary, although none the less interesting, 

 nature. 



One is, therefore, led to inquire as to whether there 

 maybe available evidence which will permit a new insight 

 into conditions governing the formation of characters, 

 even though the evidence from its nature must be Largely 

 circumstantial. 



IV 



Accompanying- the progressive swimming movement 

 of most aquatic microorganisms there is a characteristic 

 axial rotation. This has been noted by Nageli, Engel- 

 mann, Strassburger, Mast and more in detail by Jennings 

 (1901) who has called attention to the value which such a 

 compensatory motion may have for the organism in which 

 it exists. No explanation has been suggested other than 

 this as to the origin of the rotation, and without further 

 thought it is evident that one. would be inclined to attrib- 

 ute it to natural selection, assuming that those individ- 

 uals in which it did not occur were at a disadvantage in 

 the struggle for existence by reason of their more con- 

 fined movement. 



It is the phase of the question dealing with the par- 

 ticular causes bringing about the rotation that appears 

 to be of extreme significance when considered in connec- 

 tion with the principles underlying evolution and to be 



