CHAP. XI! r.] 



THE GALAPAGOS ISLANDS. 



2&7 



tiiose 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 rela^tion 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 uniaiportant 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 

 numb>er 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 afPmities of so many of 

 the plants, and even of some of the birds. The relation between 

 the migratory habits of the birds and the am.ount of difference 

 from conti]iental types is strikingly accordant with the fact that 



