268 



THE AMEBIC AN NATURALIST 



[Vol. XLII 



factors in evolution are more commonly held as dominant 

 by those who regard species as indefinite things gradually 

 evolved from other species. In this connection it is 

 curious to note that the idea of a species as an entity, 

 now held by most mutationists, has much in common 

 with pre-Darwinian notions of special creation; it seems 

 to 'be in part a return to former conceptions of a rigid 

 nature. On the other hand a new idea of species content 

 is set up. Both pre-I)arwinians and Darwinians agreed 

 that Draba verna is a species, but the new school would 

 maintain that under this name are masquerading a hun- 

 dred odd real species. 



There are, then, two radically different conceptions of 

 species now current, one of a rank as much higher than 

 the other as the genus is above the Linnean species, or 

 the family above the genus. Ecological observations 

 support both views, but it is especially the experimental 

 method that has made things clear. Whether or not 

 one calls them species, it is evident that the genus 

 Oenothera contains a number of entities, sharply defined 

 from one another. In such genera as Salix and Aster 

 there is reason to believe that species do not thus differ 

 sharply, but that they are connected with one another by 

 all but imperceptible gradations ; at any rate this condi- 

 tion exists in Leptinotarsa, as conclusively shown by 

 Tower. It seems impossible to homologize species in 

 (Enothera and Leptinotarsa. It appears that the method 

 of evolution in various groups of plants and animals is 

 radically different, and it follows as a corollary that 



sarily not homologous. * gl ° UpS 



In the light of these views the task of the taxonomist 

 is seen to be most difficult; for the convenience of biol- 

 ogists, he must reduce to common terms things that are 

 unrelated; he must homologize things that are not homol- 

 ogous. In such a dilemma there seem two courses open: 

 (1) The Linnean species concept, that has ruled both 

 before and after evolution was accepted by biologists, 



