144 THE SHORTER SCIENTIFIC PAPERS 



formed in the *'X" chromosome and merely awaits a 

 suitable environment before presenting itself as a char- 

 acter. Similarly, in connection with the changes occur- 

 ring in the development of the **free-martin" of cattle, 

 it seems necessary to admit that there are genes present 

 in the sex chromosome concerned with the development 

 of sexual characters which, however, are in a state of 

 equilibrium, and that the inhibition or the excitation^ of 

 one or the other genes or groups of genes will result in 

 the development of the corresponding individual. 



From the facts presented, one seems justified in making 

 the deduction that heredity hands down a framework 

 which within certain limits allows a plasticity in the 

 development, and that the direction of development is 

 determined by physio-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 

 results of a secondary, although none the less interesting, 

 nature. 



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

 be 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 cir- 

 cumstantial. 



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 



^It has been shown by Chapin (1917) that the gonads of the free-martin 

 originally destined to be a female, attain a male condition. 



