282 Proceedings of the Royal Society 
decorated ; and in many instances most resplendent in colour. My 
own opinion is, that this gorgeous colouring of the humming-birds 
has been given for the mere purpose of ornament, and for no other 
purpose of special adaptation in their mode of life ; in other words, 
that ornament and beauty, merely as such, was the end proposed.”* 
Different parts of the plumage have been selected in different 
genera as the principal subject of ornament. Tn some, it is the 
feathers of the crown worked into different forms of crest ; in some, 
it is the feathers of the throat, forming gorgets and beards of many 
shapes and hues ; in some, it is a special development of neck 
plumes, elongated into frills and tippets of extraordinary form and 
beauty. In a great number of genera the feathers of the tail are the 
special subjects of decoration, and this on every variety of plan and 
principle of ornament. In some, the two central feathers are most 
elongated, the others decreasing in length on either side, so as to 
give the whole the wedge form. In others, the converse plan is 
pursued, the two lateral feathers being most developed, so that the 
whole is forked after the manner of the common swallow. In 
others, again, they are radiated, or pointed and sharpened like thorns. 
In some genera there is an extraordinary development of one or 
two feathers into plumes of enormous length, with flat or spatulose 
terminations. Mere ornament and variety of form, and these for 
their own sake, is the only principle or rule with reference to which 
Creative Power seems to have worked in these wonderful and beau- 
tiful birds. And if we cannot account for the differences in the 
general style and plan of ornament followed in the whole group, 
by referring them to any sort of use in the struggle for existence, 
still less is it possible to account, on this principle, for the kind of 
difference which separates from each other the different species in 
each of the genera. These differences are often little more than 
a mere difference of colour. The radiance of the ruby or topaz in 
one species, is replaced perhaps by the radiance of the emerald or the 
sapphire in another. In all other respects the different species are 
sometimes almost exact counterparts of each other. As an ex- 
ample, let me refer to the two species figured by Mr Gould as the 
Blue-tailed and the Green-tailed Sylphs ; and also to two species 
* Gould’s “ Trochilid?e,” Introduction. 
