204 Mr. A. R. Wallace on the Natural Arrangement of Birds. 



that of a Swallow lengthened out to contain the long and exten- 

 sile tongue ; and the vital force and energy which enables the 

 Swallows to enjoy such long-continued and rapid motion, seems 

 here to have reached a point beyond which further development 

 is scarcely possible. How then can we refuse them a place 

 among those birds of which they possess the distinctive cha- 

 racters in the most eminent degree, while at the same time we 

 keep together birds as different from each other as the King- 

 fisher from the Swallow, because they possess those characters ? 

 But it will be objected that the structure of the tongue is so 

 different and peculiar, and agrees so well with that of the Sun 

 Birds. But we have already mentioned, and again repeat, that 

 in closely allied genera of Sun Birds the tongue is totally dif- 

 ferent, and that therefore it is not a character to outweigh the 

 whole structure and habits of a group of birds : moreover, in 

 other groups the same difference in the tongue is not held to be 

 sufficient to separate birds otherwise allied. The Cuckoos and 

 the Toucans have ever been placed near each other, yet how dif- 

 ferent their tongues ! while the Woodpeckers, still farther differ- 

 ing from them, are notwithstanding placed in the same tribe of 

 Climbing birds. We might also expect, that when the structure 

 of a bird had become so peculiarly modified as to bring it to seek 

 the same food in the same places as another bird of quite a dif- 

 ferent type of structure, we should find each of them gifted with 

 the same peculiarly modified organ adapted to such habits ; and 

 we therefore find that the Sun Birds and the Hummers, though 

 with a widely different general structure, yet have a similarly 

 constructed tongue which they both use in extracting minute 

 insects from flowers and leaves. An exactly analogous instance 

 exists in the Picid^e and Dendrocolaptida, two families as different 

 in general structure as the Trochilida and Nectarinidce, but which 

 yet have one striking similarity in the rigid tail, which enables 

 them both to rest vertically against a tree while extracting insects 

 from the bark. We contend that these cases are strictly ana- 

 logous, and that there is no more real affinity in the one case 

 than in the other. The character which is most opposed to this 

 view of their affinities is their nidification ; but we think this is 

 not only not an insuperable obstacle to their being thus placed, 

 but one that we might to some degree have anticipated. In 

 some of the Swallows we have already seen one deviation from 

 the general character of the tribe in the carefully constructed 

 nest of clay. In the Goatsuckers we have another, the Podargus 

 of Australia forming a nest of sticks and grass on the branches 

 of a tree. We should therefore expect that birds so peculiarly 

 and highly organized as the Hummers, so aerial in their habits, 

 and so intimately associated with flowers and foliage, would have 

 a modified and characteristic form of nidification. 



