No. 610] MUTATION THEORY AND SPECIES-CONCEPT 591 



occurred. However, the process does appear to be 

 gradual at least in comparison with the other type of 

 variability, which is fundamentally different in its geo- 

 graphic relations. 



The second type of variability in Otus asio to which I 

 have reference, consists in the occurrence of gray and 

 reddish or rufous phases of coloration in the same area 

 of distribution. Thus all the eastern subspecies, asio, 

 ncBvius, mccallii and hashrouchi, produce both gray and 

 red birds. These phases are sharply marked, and inter- 

 mediates rarely occur. Hasbrouck^^ attempted an ex- 

 planation of this dichromatic condition, but some of his 

 conclusions were justly criticized by Allen.^^ The gray 

 phase occurs more commonly in Florida and in the north- 

 ern part of the range of nccvius,^^ while the red phase oc- 

 curs commonly in the Central Atlantic states, perhaps 

 to the exclusion of the gray in some localities. The red 

 phase is unknown in the western forms of Otus asio. 

 Nevertheless grayish and rufescent phases of the small 

 0. fammeolus, which is found in the mountains of western 

 America from British Columbia to Mexico, occur in this 

 region. The red phase is found also in 0. trichopsis 

 (see map). Similarly, brown and rufous phases are 

 found in 0. choliba which extends over a large part of 

 South America, and also in the Central and South Amer- 

 ican species 0. cassini, 0. guatamalce, 0. harhariis and 0. 

 vermiculatus. 



Owls belonging to other genera also exhibit two phases. 

 For example Bubo virginianus {Asio magellanicus),^^ the 

 single species of Buho occurring in all North and South 

 America, with many geographic varieties, shows dichro- 

 matism in various parts of its range. The same is ap- 

 parently true of various Old World owls. 



1- Hasbrouck, E. M., 1893, "Evolution and Dichromatism in the Genus 

 Megasc(yps," Ameb. Nat., 27:521-533, 63S-649, 4 maps. 

 IS A(llen), J. A., 1893, Aul; 10: 347-351. 



19 Oberholser, H. C, 1904, "A Eevision of the American Great Horned 

 OtvIs," Proc. U. S. Nat. Mus., 27: 177-192. 



20 The red phase is stated by Allen to be rare in Maine. 



