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THE AMERICAN NATURALIST [Vol. XLIX 



" mutation of Waagen" would appear as a Linnaean 

 ''species" when compared by an observer with, contem- 

 porary mutations in other phyla; that is, each phylum 

 may be separated from contemporaneous phyla by valid 

 Linnaean characters. 



The essence of Waagen 's discovery is that when we 

 observe the origin and evolution of single characters in 

 time we are able to detect the incipience of new charac- 

 ter* and tlx profound h c red ii n r// plii/hdie movements 



which can not be observed by the zoologist at all. We 

 are able, moreover, to distinguish the minute and even 

 inconspicuous characters, which are evolving in definite 

 directions and accumulating in successive generations, 

 from the indefinite and transitory characters of the geo- 

 graphic "variety." The underlying cause of this dis- 

 tinction in the light of our present knowledge is that mu- 

 tations denote germinal or phyletic evolution while vari- 

 eties may simply denote the bodily fluctuations caused by 



