CIIAP. XIII.] 
THE GALAPAGOS ISLANDS. 
297 
those more remote from the coast; but unfortunately our know- 
ledge of the productions of the various islands of the group is 
exceedingly unequal, and, except in those cases in which repre- 
sentative species inhabit distinct islands, we have no certainty 
on the subject. All the more interesting problems in geogra- 
phical distribution, however, arise from the relation of the fauna 
and flora of the group as a whole to those of the surrounding 
continents, and we shall therefore for the most part confine 
ourselves to this aspect of the question in our discussion of the 
phenomena presented by oceanic or continental islands. 
Concluding Remarks . — The Galapagos offer an instructive 
contrast with the Azores, showing how a difference of condi- 
tions that might be thought unimportant may yet produce very 
striking results in the forms of life. Although the Galapagos 
are much nearer a continent than the Azores, the number of 
species of plants common to the continent is much less in the 
former case than in the latter, and this is still more prominent 
a characteristic of the insect and the bird faunas. This differ- 
ence has been shown to depend, almost entirely, on the one 
archipelago being situated in a stormy, the other in a calm, 
portion of the ocean ; and it demonstrates the preponderating 
importance of the atmosphere as an agent in the dispersal of 
birds, insects, and plants. Yet ocean-currents and surface-drifts 
are undoubtedly efficient carriers of plants, and, with plants, of 
insects and shells, especially in the tropics ; and it is probably to 
this agency that we may impute the recent introduction of a 
number of common Peruvian and Chilian littoral species, and 
also at a more remote period of several West Indian types when 
the Isthmus of Panama was submerged. 
In the case of these islands we see the importance of taking 
past conditions of sea and land and past changes of climate into 
account, in order to explain the relations of the peculiar or ende- 
mic species of their fauna and flora ; and we may even see an 
indication of the effects of climatal changes in the northern hemi- 
sphere, in the north temperate or alpine affinities of so many of 
the plants, and even of some of the birds. The relation between 
the migratory habits of the birds and the amount of difference 
from continental types is strikingly accordant with the fact that 
