402 



CHARLES DARWIN 



that of a warbler. The largest beak in the genus Geospiza 

 is shown in Fig. i, and the smallest in Fig. 3; but instead of 

 there being only one intermediate species, with a beak of 

 the size shown in Fig. 2, there are no less than six species 

 with insensibly graduated beaks. The beak of the sub-group 

 Certhidea, is shown in Fig. 4. The beak of Cactornis is 



i. Geospiza magnirostris. 

 3. Geospiza parvula. 



2. Geospiza fortis. 

 4. Certhidea olivasea. 



somewhat like that of a starling; and that of the fourth sub- 

 group, Camarhynchus, is slightly parrot-shaped. Seeing this 

 gradation and diversity of structure in one small, intimately 

 related group of birds, one might really fancy that from an 

 original paucity of birds in this archipelago, one species had 

 been taken and modified for different ends. In a like manner 

 it might be fancied that a bird originally a buzzard, had been 

 induced here to undertake the office of the carrion-feeding 

 Polybori of the American continent. 



Of waders and water-birds I was able to get only eleven 

 kinds, and of these only three (including a rail confined to 

 the damp summits of the islands) are new species. Consid- 

 ering the wandering habits of the gulls, I was surprised to 

 find that the species inhabiting these islands is peculiar, but 

 allied to one from the southern parts of South America. 



