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 completcly 
unchanged in the Galapagos ; and we may therefore 
conclude that some stragglers of the migrating host 
reach the islands sufficiently oftcn 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 gencra 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 35 
1 Wallace, /sland Life, pp. 271-2. 
