264 The Naturalist in La Plata. 



select males for their superiority in some aesthetic 

 quality, such as graceful or fantastic motions, 

 melody of voice, brilliancy of colour, or perfection 

 of ornaments. Doubtless all birds were originally 

 plain-coloured, without ornaments and without 

 melody, and it is assumed that so it would always 

 have been in many cases but for the action of this 

 principle, which, like natural selection, has gone on 

 accumulating countless small variations, tending to 

 give a greater lustre to the species in each case, and 

 resulting in all that we most admire in the animal 

 world — the Rupicola's flame-coloured mantle, the 

 peacock's crest and starry train, the joyous melody 

 of the lark, and the pretty or fantastic dancing 

 performances of birds. 



My experience is that mammals and birds, with 

 few exceptions — probably there are really no excep- 

 tions — possess the habit of indulging frequently in 

 more or less regular or set performances, with or 

 without sound, or composed of sound exclusively; 

 and that these performances, which in many animals 

 are only discordant cries and choruses, and uncouth, 

 irregular motions, in the more aerial, graceful, and 

 melodious kinds take immeasurably higher, more 

 complex, and more beautiful forms. Among the 

 mammalians the instinct appears almost universal ; 

 but their displays are, as a rule, less admirable 

 than those seen in birds. There are some kinds, 

 it is true, like the squirrels and monkeys, of arbo- 

 real habits, almost birdlike in their restless energy, 

 and in the swiftness and certitude of their motions, 

 in which the slightest impulse can be instantly ex- 

 pressed in graceful or fantastic action ; others, like 



