152 
sexual selection: birds. 
PA ** 1 
passes over sexual selection, and asks, « What expl^l 
“ l' 011 ^oes the law of natural selection give of ® u ^ 
“specific varieties as these?” He answers “» 0l J 
“whatever;” and I quite agree with him. Bid ^ 
this be so confidently said of sexual selection ? S^'f, 
in how many ways the tail-feathers of humming' 1 " 1 ' 1 .' 
differ, why should not the four central feathers 
varied in this one species alone, so as to have acq^ 
white tips? The variations may have been gradin'*’^ 
somewhat abrupt as in the case recently given of 
humming-birds near Bogota, in which "certain ifl j 
viduals alone have the “central tail-feathers tipf, 
“with beautiful green.” In the female of the • r '.^ 
ticte 1 noticed extremely minute or rudiments! 
tips to the two outer of the four central black t:1 ‘ , 
feathers ; so that here we have an indication of ch a "h 
of some kind in the plumage of this species. If we g 1 ’ 8 ,, 
the possibility of the central tail-feathers of the 
varying in whiteness, there is nothing strange in sll ! ft . 
variations having been sexually selected. The 
tips, together with the small white ear-tufts, cori^ 1 ' 1 ! j 
add. as the Duke of Argyll admits, to the beauty 0 * j' r 
male ; and whiteness is apparently appreciated by ot ^ 
birds, as may be inferred from such eases as the ^ 
w hite male ot the Bell-bird. The statement ni^d' 3 . 
Sii h. Heron should not be forgotten, namely that 
peahens, when debarred from access to the pied pe^ 0 .^ 
would not unite with any other male, and during 1 K t 
season produced no offspring. Nor is it strange f'b 
variations in the tail-feathers of the Urosticte 
liave been specially selected for the sake of ornao 1 ' 8 ., 
toi the next succeeding genus in the family tak° B ^ 
name ofMetallura from the splendour of these featl*' , 
Mr. Gould, after describing tlie peculiar plumage of ^ 
Uiosticte, adds, 1 that ornament and variety is the 
