'JOo Trotter on the Genus Hclminthophila. [ October 



Virginia and Itccice are restricted in their ranges, being char- 

 acteristic of the Colorado Valley and Southern Rocky Mountain 

 region. 



The other section comprises bachmani, chrysofitera, pinus, 

 and their curious allies, lawrencei and leucobronchialis ; birds of 

 striking coloration and of much more restricted ranges than the 

 three plainer colored species of the former sub-group. Bachmani 

 is exceedingly rare, having been taken but a few times in the 

 Southern States. The Blue Golden-winged Warbler, chry- 

 soplera, and the Blue-winged Yellow Warbler, pimis, are 

 exclusively birds of the Eastern Province, the former ranging 

 into Canada, though rarer in the Northern States, the latter 

 scarcely if ever going beyond Massachusetts and Minnesota. 

 Both winter south of our limits. 



I have taken the liberty of thus hastily reviewing the genus for 

 the purpose of bringing together as nearly as possible our present 

 knowledge of the distribution of the several species. The history 

 of the two forms lawrencei and leucobronchialis is already so 

 well known to ornithologists that it need not be reiterated here, 

 except to recall the very general belief of their hybrid nature. 



The question naturally arises in the minds of most persons 

 who have given any thought to the subject, What does the oc- 

 currence of such peculiar forms, taken in conjunction with other 

 facts, signify? We are stepping into a somewhat uncertain re- 

 gion when we attempt to speculate on a subject of this character, 

 but I believe that the only way in which we may hope to throw 

 any light whatever upon such a subject is from an evolutionary 

 standpoint. 



The rise and decay of genera and species in the struggle for 

 existence ; the pressure of dominant groups upon smaller and 

 less adapted races ; action and reaction through environment ; — 

 these are the factors involved, and that have given rise to many 

 apparently inexplicable phenomena. 



A dominant group is characterized by the abundance of its 

 forms, both in species and individuals, over wide areas, this being 

 the index of its vigor and consequent ability to maintain itself 

 against competitors, and its adaptability to varying conditions of 

 environment. Rarity in species and individuals is indicative of 

 degeneracy, the expression of the inability of the gi'oup to hold 

 its own. 



