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1 2 Evolution and Adaptation 



much more distinct from the western forms than these are 

 from each other. 



Finally may be mentioned the curious variations in 

 screech-owls of the genus Scops. This owl has two strik- 

 ingly different plumages — a mottled gray and a reddish 

 brown, which, although very distinct when fully developed, 

 vet "are entirely independent of age, season, or sex." There 

 Is an eastern form, Scops asio, that extends west to the 

 Rocky Mountains. There is a northwestern form, S. keimi- 

 cotti, which in its red phase is quite different from 5. asio, 

 but in its gray plumage is very similar. The California form, 

 5. bcnderii, is not known to have a red phase, and the gray 

 phase is quite different from that of 5. asio, but like the last 

 form. The Colorado form, 5. maxwella, has no red phase, 

 " but on the contrary the whole plumage is very pale, almost 

 as if bleached, the difference evident in the nestlings even." 

 The Texas form, 5. maselli, has both phases, and is very 

 similar to S. asio. The Florida form is smaller and colored 

 like 5. asio. The red phase is the frequent, if not the 

 usual, one. The flammulated form, S.fiammuta, is "a very 

 small species, with much the general aspect of an ungrown 

 S. asio." This is the southwestern form, easily distinguished 

 on account of its small size and color from the other forms. 



These examples might be greatly increased, but they will 

 suffice, I think, to convince one of the difficulty of giving a 

 sharp definition to "species." The facts speak strongly in 

 favor of the transmutation theory, and show us how a species 

 may become separated under different conditions into a num- 

 ber of new forms, which would be counted as new different 

 species, if the intermediate forms were exterminated. 



In discussing the nature of the changes that bring about 

 variability, Darwin remarks : " From a remote period to the 

 present day, under climates and circumstances as different 

 as it is possible to conceive, organic beings of all kinds, when 

 domesticated or cultivated, have varied. We see this with 



