THE EVOLUTION OF BIRD-SONG. 283 



The skin of the Xenopus was, as already stated, rendered 

 glassy and transparent under the sudden drain upon its resources ; 

 and I was struck with the fact that certain dark blotches con- 

 spicuous upon it at other times were little perceptible, owing no 

 doubt to the over-contraction of the chromatophores composing 

 them. Concerning these darker areas of the Amphibian integument 

 Mr. Poulton records some interesting observations, and while he 

 concludes (p. 85) that a " connection between the nerves and the 

 pigment-cells in the skin . . . appears to be rendered certain by the 

 fact that light falling on the eye modifies the distribution of the 

 pigment granules," he states that " the highest powers of the micro- 

 scope, assisted by all the varied methods of histology, have failed 

 to detect" it. There is, however, no reason for conjecture; for, 

 while Leydig has seen and described the connection in Lizards, 

 Ehrmann (Stzb. Wien Akad. Math. Nat. CI. Bd. 84, Abth. 3, 

 p. 165, 1881), and Haller (Zoolog. Anz. 1885, p. 611), have inde- 

 pendently observed and figured it in the Common Frog. 



SUPPLEMENTARY NOTES ON THE EVOLUTION OP 



BIRD-SONG.* 



By Charles A. Witchell. 



The imitative tendency of many species of wild birds is 

 indicated by the mimicry of captive individuals, which is often 

 very apparent, but is limited to imitations of noises with which 

 they are familiar. Ornithological works generally do not dis- 

 tinguish with sufficient accuracy the songs of captive and wild 

 individuals, which are not usually the same. It will be observed 

 that the rearing of the young influences song ; for, when this is 

 about, some species, such as the Nightingale, Kedstart, Willow 

 Warbler, Chiflchaff, Wood Warbler, Blackbird, and Missel Thrush, 

 utter very frequently their alarm-cries, and neglect their songs ; 

 while the Sky Lark and Tree Pipit fly less often during song, 

 and in a great measure abandon those long-drawn notes (closely 

 like the call-note of the young Sky Lark) which form in early 

 spring the endings of their phrases. At the same time the 



* See antea, p. 233, 



y3 



