THE BIEDS OF SABK. 421 



quite impossible, where so many dialects probably exist, and 

 where so little is known about any one of them, to fix any 

 standard. I would, therefore, suggest that comparisons should 

 be made under as diverse conditions as possible— that is to say, 

 between very wet and very dry districts, or between districts 

 inland and districts on the coast. If it can be proved that this 

 variation exists among certain migratory species immediately 

 on arrival in this country, it will be necessary to follow them 

 into their winter quarters. For, supposing a dialect is inherent 

 in any one given species (which at first seems almost incredible), 

 we should expect to see some signs of it in their said winter 

 quarters. On the other hand, if we follow them and again find 

 new dialects and new gradations of tone, or if we find on their 

 arrival in this country that there is no immediate variation, but 

 that it increases as the season advances, we shall have strong 

 evidence that in some measure at least it is directly due to 

 climatic influence. 



I have shown that so many and such distinct variations do 

 exist, and it seems only reasonable to expect that some of these 

 variations, amongst those species which are resident, will become 

 hereditarily attached to the male sex — for if they did not it would 

 be subversive of the theory of sexual selection, a theory which 

 must be admitted by all those who have studied certain species, in 

 whom the vocal powers are excessively developed while courting 

 — consequently species with a certain variety of song will exist 

 in a small body and often breed together, and as a result the 

 development from a dialect to specific song must in time ensue. 

 It may be argued that it is impossible for a variety of song 

 amongst individuals of any one species to have any connection 

 with the origin of song in separate species ; but I can see no 

 more difficulty in believing, except to those, if there are any, 

 who still look upon species as immutable, that through the vast 

 ages that have lapsed, during which species have developed, a 

 specific song may have become attached to a certain species 

 through the action of sexual selection on varieties resulting from 

 climatic influence, than I can in believing that species them- 

 selves have been evolved. 



When we reflect on these variations of song, we can easily 

 understand what mistakes have arisen, and probably will arise, 



