Geographical Distribution. 229 



less than 38 are peculiar ; and all the non-peculiar 

 species, except one, belong to aquatic tribes. The 

 true land-birds are represented by 31 species, of 

 which all, except one, are peculiar ; while more than 

 half of them go to constitute peculiar genera. More- 

 over, while they are all unquestionably allied to 

 South American forms, they present a beautiful 

 series of gradations, " from perfect identity with the 

 continental species, to genera so distinct that it is 

 difficult to determine with what forms they are most 

 nearly allied ; and it is interesting to note that this 

 diversity bears a distinct relation to the probabilities 

 of, and facilities for, migration to the islands. The 

 excessively abundant rice-bird, which breeds in 

 Canada, and swarms over the whole United States, 

 migrating to the West Indies and South America, 

 visiting the distant Bermudas almost every year, 

 and extending its range as far as Paraquay, is the 

 only species of land-bird which remains completely 

 unchanged in the Galapagos ; and we may therefore 

 conclude that some stragglers of the migrating host 

 reach the islands sufficiently often to keep up the 

 purity of the breed ^" Again, of the thirty peculiar 

 land-birds, it is observable that the more they differ 

 from any other species or genera on the South 

 American continent, the more certainly are they found 

 to have their nearest relations among those South 

 American forms which have the more restricted 

 range, and are therefore the least likely to have found 

 their way to the islands with any frequency. 



The insect fauna of the Galapagos islands is scanty, 

 and chiefly composed of beetles. These number 'ifS 

 ' Wallace, Zf/a«</ Zy^, pp. 271-2. 



