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THE AMERICAN NATURALIST [Vol. XLIX 



It has now been made clear why these stages are recog- 

 nizable and definable by the paleontologist and not by the 

 botanist, zoologist or experimentalist. 



To sum up the observations of zoologists and pale- 

 ontologists with regard to the single property of the 

 movement of characters in progressive organisms the 

 following principles are observed: 



All characters are in simultaneous movement; such 

 movements are differential, each character has its own 

 rate ; some movements are ontogenic or with a velocity- 

 relation to other characters in the same individual; others 

 are phyletic or with a velocity-relation to similar charac- 

 ters in other species and genera; "least-character" 

 movements are continuously progressive or retrogres- 

 sive; certain least-characters are stationary; "least-char- 

 acter" movements may develop or manifest a certain 

 direction or trend, the M ittatioi/sriclitung, and thus may 

 be cumulative to an extreme; all character movements 

 which are cumulative in successive generations have a 

 germinal or hereditary basis. Thus differential move- 

 ment is one of the most distinctive and important proper- 

 ties of the "character." 



This principle of continuous germinal change which 

 appears to underlie the continuous development of visible 

 bodily characters may prove to be in harmony with 

 rather than in opposition to the law through which some 

 characters appear suddenly, or by saltation. As I 

 pointed out many years ago, there may be an apparent 

 but not a real contrast between the "mutations of 

 Waagen" and the "mutations of De Vries." If the 

 former rise through continuous germinal changes and 

 the latter rise through discontinuous germinal changes 

 the common element in both may be the Mutat'umsrU-ht- 

 ung, or trend of development. In Waagen 's law this 

 trend of development appears to express itself in a con- 

 tinuous change of visible somatic development of charac- 

 ters. In De Vries 's observations the change is believed 

 to be discontinuous, suddenly constituting the "mutant" 



