658 THE POPULAR SCIENCE MONTHLY. 



horns of several ruminants, the tail-coverts of the peacock, and the 

 lappets or crests of many hirds, apparently devoid of any functional 

 use whatsoever, unless that use be the attraction of the opposite sex. 

 They are also marked by the extreme definiteness of their shape, color, 

 or sculpture a definiteness which never occurs in similar structures 

 among the lower animals. For though some echinodermata, as for 

 example the sea-urchins, are very beautifully and regularly marked, 

 yet their markings are purely dependent upon the structural arrange- 

 ments of the animal, and can not generally be detected till after death. 

 So, too, the shells of many mollusca, such as scalaria and the murices, 

 are very beautifully sculptured ; but this sculpture is structurally neces- 

 sary for the animal, and apparently depends entirely upon the shape 

 and markings of the mantle. Among birds, however, as among the 

 ruminants, all the structures ascribed by Mr. Darwin to sexual selec- 

 tion are marked by a kind of definiteness, quite unconnected with 

 ordinary functions, which it is difficult to describe in words, but which 

 can immediately be felt if we compare the coloration of a peacock 

 with that of a sea-anemone or a medusa. The former is perfectly 

 definite without being obviously connected with structure ; the latter 

 is very indefinite, and yet bears a clear relation to the general shape 

 of the animal. This combination of great specific distinctness with 

 little apparent functional value appears to me the genuine hall-mark 

 of organs due to sexual selection. 



There is even some little external evidence in favor of a love for 

 symmetry among birds. The nests of weaver-birds and many other 

 species, as well as the bowers of the bower-birds, display a consider- 

 able taste for orderly arrangement. For one must remember that the 

 building of such nests, though doubtless instinctive and inherited, is 

 not a mere organic process, like the secretion of a molluscan shell ; it 

 is as much an art as the building of a honeycomb or of a savage hut. 

 The flight of birds in play, the antics of many humming-birds, the 

 strange eddyings and aerial evolutions of several other species, all 

 approach very nearly to our own idea of dancing. I am almost afraid 

 to hazard the observation, yet on the other hand I can not avoid risking 

 it, that the attitudes taken up by the turkey-buzzards or Johncrows of 

 the West Indies upon the tops of houses frequently seemed to me in- 

 tentionally symmetrical. I have observed them sitting in every va- 

 riety of position one at each end of a long roof ; one at each of the 

 two points half-way between ends and middle ; three arranged in 

 either of these forms, with one in the middle ; five arranged in the 

 order C, B, A, B, C, etc. If any other observer can supplement this 

 experience, which I record with great diffidence, I shall be very glad. 



Taking for granted, then, this appreciation of form and symmetry, 

 we shall find that it has produced many notable effects in the world 

 of birds. To it, apparently, we owe the crests of cockatoos, pigeons, 

 herons, and a hundred other species ; the wattles, combs, hackles, and 



