S6 Lawrence's wakblek, 



tincllv savs, " . . . . there is seldom, if ever, an indication of the black throat of H, 

 rhrysoftera.'' ( It may be remarked, however, that it is not at all certain, judging 

 from what is known of the subject, that the hybrid offspring of closely allied species 

 among birds would show perfect intergradation. There is much evidence to show 

 that they might be quite similar to either parent). Why also do we not find some 

 specimens of Lawrence's partly gray or white ? Both of these characters should ap- 

 pear in perfect intergrades. Then again, why do a large proportion of both Brews- 

 ter's and Lawrence's show the peculiarly formed white spot on the inner web of the 

 second tail feather that is characteristic of the Golden- wing? This character should 

 also intergrade. lam now writing, I inustagain remark, without an exact knowledge 

 of just what intergradation Mr. Brewster has seen when he speaks of " complete in- 

 tergradation ". 



In regard to the second point, I n>ay say that I have carefully gone over the 

 evidence given, and can in every case see a chance for mistakes. In short, I think 

 we need clearer evidence, checked by trained observers, before we can positively af- 

 firm that the Golden-winged and Blue-winged Warblers mate together or with ei- 

 ther Brewiiter's or Lawrence's. 



Now in regard to the third point, although Brewster's and Lawrence's Warb- 

 lers do occur in a portion of the region where the breeding range of the Golden-wing 

 and Blue-wing overlap, they do not occur all over it, but are confined to a limited 

 section of it, excepting as mere stragglers. Thus Brewster's Warbler occurs only in 

 southern Connecticut, the lower Hudson River Valley, northern New Jersey, south- 

 eastern Pennsylvania, and north-eastern Virginia; thus leaving southern-central and 

 western Penns_\ Ivania, central Ohio, northern Indiana, central Illinois, and south- 

 eastern Iowa of the section overlapped without the so-called hybrids. Lawrence's 

 occupies even a much smaller area. If the Golden-wings and Blue-wings produce 

 hybrids in one portion of the region where the two species overlap, why do they not 

 produce hybrids in all? 



In discussing the fourth point it may be said that Brewster's Warbler sings in 

 varying Avays is no more proof that it is a hybrid than that it is an incipient species 

 the oft'spring of the Golden-wing, for the song would be no more fixed than thecolor» 

 and reversion toward the ancestral types mentioned below would naturally cause va- 

 riation in the song. 



'I'he most fatal objection to the hybrid theory is the well known law, proved by 

 experiment in several ways, that different species of birdseven of the same genus when 

 mated together are seldom fertile, and when fertile their offspring are almost never 

 capable of reproducing, especially when breeding inter sc. A little reflection will 

 show us that were it not for such a law closely allied species could not exist in close 

 proximity, for were hybridization with fertility possible they would soon intergrade 

 completely. While it is true that closely allied speciesdo not often overlap, or other- 

 wise mingle on their breeding grounds, they sometimes do, witnessfor example, the 

 genus Geofhlyph on the island of New Providence, Bahamas, where at least three 

 perfectly distinct yet closely allied species intermingle completely, but as far as known 

 without hybridizing. Our own Chipping and Field Sparrows also oflera familiar ex- 

 ample of this overlapping of closely allied species, and we do not find these species 

 hybridizing. 



Taking up Mr. Ridgeway's theory of dichromatism, we have only to ask why 

 does not dichroniatisrm occur everywhere among both the Golden-wings and Blue 



