134 ORTHOGENETIC EVOLUTION IN PIGEONS. 



Studying the marking in the various feather-tracts, Kerschner found that color differ- 

 entiations went hand in hand with an "increase in the number of elements of the tracts," 

 as Wallace maintained was the case in respect to the size and form of the ornamental 

 feathers. 



Kerschner admits that he finds among the ' ' tail-coverts of the peacock some feathers 

 with paired ocelli." If Darwin had seen these he would have considered them strong 

 evidence in favor of his view. Kerschner still holds, however, that these cases are not 

 "phyletic stages," but rather "stages of degeneration." The complete developmental 

 series is said not to show these double stages. 



The results of this investigation contradict Eimer's law that longitudinal striping 

 precedes cross-barring. "Eimer's law of postero-anterior development," if applicable to 

 feathers, should become the "law of antero-posterior development" (page 690). But even 

 in this form the law would not hold according to Kerschner, neither in respect to the entire 

 plumage nor to the single feathers. He thinks the differentiations occur in many direc- 

 tions, and even in opposite directions. "For the single feather I could not find any rule, 

 although generally new characters arise near the apex, while the apex itself retains the 

 older characters, and the covered portions of the feather usually show the more original 

 marking." But he finds many exceptions even to this. Against Eimer's wave-law Kersch- 

 ner asserts: "The development of the new characters of a series, viewed as motion, is 

 always in a straight line." 



FURTHER EXAMPLES OF THE TURTLE-DOVE PATTERN AND ITS DERIVATIVES IN BIRDS. 



Dark Centers. 



In the genus Anas are included species which retain the dark centers, and others 

 with barring carried out to a very high degree. These species often show, also, a 

 higher modification of the ancestral pattern in the males than in the females. 



(1) In the blue-winged teal 37 {Anas discors Linnaeus) the male has the lower part 

 of the front-neck, the breast, and the feathers of the whole under surface with 

 dusky centers and pale rufous edges. The mantle is dark brown, with feather- 

 edges of pale rufous or gray. There are also one or two semicircles parallel to the 

 edge of the feather of the same color with the feather's edge. 



In the female the back is deeper brown, the feathers margined with yellowish 

 buff; the breast and sides are similar but paler. The belly and vent are pale yellow- 

 ish brown, but with dark centers. Over all the neck and head small dark centers 

 are present, giving a spotted appearance. The male has extra crescents in the 

 mantle feathers; the female has only the crescentic margin. 



(2) In the pintail 3s (Dajila acuta) the male is extensively and finely barred on 

 the back and wings; the female has dark centers in these same regions. 



Dark Centers and Transverse Bars. 



The central dark spots, similar to those of the turtle-dove, may break up into 

 transverse bars. I find such spots in hawks and other species. 



(1) In Falco linnunculus japonicus 30 the female has triangular spots on the lower 

 parts, and these are reduced on the neck and upper breast to elongated central 

 streaks. The wing-coverts have broad "triangular dark spots" near the ends of 

 the feathers, then a light transverse bar, and then a dark bar. The row of long 

 coverts shows this best. These three dark bars, alternating with three light ones, 



»' Buffon, Ois, Vol. IX, p. 279; <? pi. enl. No. 966; 9 pi. enl. No. 403. 



38 See Nuttall's Ornithology, Vol. II, page 309. 



39 See pi. 1, Temminck and Schlegel, Fauna Japonica, 1850. 



