290 ISLAND LIFE part ii 



explored, it might be interesting to see whether, as in the 

 case of the Azores, the number of species diminished in 

 those more remote from the coast ; but unfortunately our 

 knowledge of the productions of the various islands of the 

 group is exceedingly unequal, and, except in those cases 

 in which representative species inhabit distinct islands, we 

 have no certainty on the subject. All the more interesting- 

 problems in geographical 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 23resented by 

 oceanic or continental islands. 



Concluding Bern arks. — The Galapagos offer an instructive 

 contrast with the Azores, showing how a difference of con- 

 ditions that might be thought unimportant may yet pro- 

 duce very striking results in the forms of life. Although 

 the Galapagos are much nearer a continent than the 

 Azores, the number of species of 23lants common to the 

 continent is much less in the former case than in the latter, 

 and this is still more jDrominent a characteristic of the 

 insect and the bird faunas. This difference has been 

 shown to dej)end, 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 im- 

 j^ortance of the atmosjDhere 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 of several West Indian 

 types at a more remote period when the Isthmus of Panama 

 was submerged. 



In the case of these islands we see the importance of 

 taking account of past conditions of sea and land and past 

 changes of climate, in order to exj^lain the relations of the 

 peculiar or endemic species of their fauna and flora ; and 

 we may even see an indication of the effects of climatal 

 changes in the northern hemisj)here, in the north tern- 



