NATURAL SCIENCES OF PHILADELPHIA. 61 



tinuously subjected to local modifying influences of a special 

 kind, it preserves its peculiarities intact; specimens from the ex- 

 tremes of its range are utterly indistinguishable. But the non- 

 migratory individuals of Mexico, belonging to the same crinitus 

 stock, present recognizable local varieties; whilst M. stolidus, a 

 thoroughly localized bird, stationary in several places, has de- 

 veloped several sharply distinguished insular races peculiar to the 

 islands they respectively occupy. 1 



I can offer no satisfactory explanation of the fact that several 

 species of the genus are distinguished by the amount of rufous 

 coloring, though I suspect it may be referable to proposition e, 

 considering fuscous a "more intense" coloration than rufous. 

 Certainly the northernmost bird, crinitus, and the bird of the 

 New Mexican deserts, have the most rufous of any continental 

 forms. The extent of rufous decreases even in the Mexican varie- 

 ties of crinitus, is still less in laivrencii, and almost or quite 

 disappears in the purely tropical nigriceps, ferox, and phseocepha- 

 lus. But even continental specimens of an opposite character occur, 

 whilst the insular species, validus and stolidus, offer completely 

 rebutting testimony. 



This general question of the production of the rufous aside, 

 study of these birds makes it evident that large allowance must 

 be granted for purely individual commonly called "accidental" 

 differences in amount or intensity of the rufous in specimens of 

 the same species. Though it is certain that, for example, validus, 

 cinerascens, and crinitus, with its varieties, may each be recog- 

 nized wi/h tolerable facility by their respective patterns of the 

 rufous, whether occupying the whole, or a small part, or a different 

 part of the inner webs of the rectrices, yet it is equally certain 

 that no such slight distinctions as its occupying a fourth, a fifth, 

 or a sixth of the web, fading insensibly or changing abruptly into 

 the fuscous, etc., can be relied upon at all. Among the varieties 

 of M. stolidus, indeed, we can trace the restriction of the rufous 

 by insensible degrees, from its occupying two-thirds of the inner 

 web to its narrow edging of the feather, and finally to its forming 

 a mere trace at the end. Moreover, the rufous differs so much in 



1 Cf. remarks upon the more stationary forms of Aegiothus, as compared 

 with the most nomadic individuals (linarius) of the genus. Coues, P. A. 

 N. S. P. 1869, p. 182, et seq. 



1812."] 



