ORIGIN OF SONG 155 



of different species ; some are harsh and others 

 monotonous, and some strike the imagination 

 by their novelty whilst others are melodious ; 

 and to the naturalist each, in its particular 

 way and in a particular degree, probably makes 

 some appeal according to the associations that 

 it arouses. But just why a Marsh- Warbler 

 is gifted with a voice that is so beautiful and 

 varied, whilst the Grasshopper- Warbler must 

 perforce remain content with a monotonous 

 trill ; just why the tail feathers of the Snipe 

 have developed into an instrument, whilst the 

 Pied Woodpecker has developed muscles which 

 enable it to make use of a decayed branch as 

 an instrument — we know no more than we do 

 of the nature of the forces which lead the Keed- 

 Warbler to weave its nest to reeds, or the 

 caterpillar of the Elephant Hawk Moth to 

 assume so peculiar an attitude when disturbed. 

 When therefore I speak of the origin, I do 

 not refer to the mode of origin of variation ; 

 I take for granted that variations somehow 

 arise, and I seek to ascertain whether there 

 is anything in the phenomena which we have 

 explored which might reasonably be held to 

 determine the survival of this one in preference 

 to that. 



When we reflect upon the problem of song 

 and consider the numerous and diverse forms 

 in which it is manifested, we are apt to draw 

 a comparison between the sounds we hear 

 and those produced by musical instruments, 

 and hence to conclude that each bird is gifted 



