GALAPAGOS ARCHIPELAGO. 



[CHAP. xvn. 



group, with the exception of one species of the sub-group Cac- 

 tornis,' lately brought from Bow Island, in the low Archipelago. 

 Of Cactornis, the two species may be often seen climbing about the 

 flowers of the great cactus-trees ; but all the other species of this 

 group of finches, mingled together in flocks, feed on the dry and 

 sterile ground of the lower districts. The males of all, or certainly 

 of the greater number, are jet black ; and the females (with perhaps 

 one or two exceptions) are brown. The most curious fact is the 

 perfect gradation in the size of the beaks in the different species of 

 Geospiza, from one as large as that of a hawfinch to that of a 

 J 



1. Geospiza miignirostris. 

 3. Geospiza parvula. 



2. Gpo.-piza 1'oitis. 

 4. Certliidea olivasea. 



chaffinch, and (if Mr. Gould is right in including his sub-group, 

 Certhidea, in the main group) even to that of a warbler. The 

 largest beak in the genus Geospiza is shown in Fig. 1, 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 somewhat like that of a starling; and that of the fourth sub- 

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

 dation 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 



