520 THE DESCENT OF MAN. 



the females, from being protected in domed nests during 

 incubation, have not had their bright colors eliminated 

 through natural selection, the males often differ in a slight 

 and occasionally in a considerable degree from the females. 

 This is a significant fact, for such differences in color must be 

 accounted for by some of the variations in the males having 

 been from the first limited in transmission to the same sex; 

 as it can hardly be maintained that these differences, espe- 

 cially when very slight, serve as a protection to the female. 

 Thus all the species in the splendid group of the Trogons 

 build in holes; and Mr. Gould gives figures * of both sexes 

 of twenty-five species, in all of which, with one partial 

 exception, the sexes differ sometimes slightly, sometimes 

 conspicuously in color the males being always finer than 

 the females, though the latter are likewise beautiful. All 

 the species of king-fishers build in holes, and with most of the 

 species the sexes are equally brilliant, and thus far Mr. Wal- 

 lace's rule holds good; but in some of the Australian species 

 the colors of the females are rather less vivid than those 

 of the male ; and in one splendidly colored species the 

 sexes differ so much that they were at first thought to be 

 specifically distinct, f Mr. R. B. Sharpe, who has espe- 

 cially studied this group, has shown me some American 

 species (Ceryle) in which the breast of the male is belted 

 with black. Again, in Carcineutes, the difference between 

 the sexes is conspicuous; in the male the upper surface is 

 dull-blue banded with black, the lower surface being partly 

 fawn-colored, and there is much red about the head; in the 

 female the upper surface is reddish-brown banded with 

 black, and the lower surface white with black markings. 

 It is an interesting fact, as showing how the same peculiar 

 style of sexual coloring often characterizes allied forms, 

 that in three species of Dacelo the male differs from the 

 female only in the tail being dull- 1 'ue banded with black, 

 while that of the female is brown with blackish bars; so 

 that here the tail differ^ in color in the two sexes in exactly 

 the same manner as the whole upper surface in the two 

 sexes of Carcineutes. 



With parrots, which likewise build in holes, we find 



* See his "Monograph of the Trogonidae," first edition, 

 f Namely Cyanalcyon. Gould's ''Hand-book to the Birds of Aus- 

 tralia," vol. i, p. 133; see also pp. 130, 136. 



