CHAP. XIII THE GALAPAGOS ISLANDS 291 



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 ijnpute 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 explain 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 hemisphere, in the north tem- 

 perate or alpinr affinities of 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 

 it is almost exclusively migratory birds that annually reach 

 the Azores and Bermuda ; while the corresponding fact 

 that the seeds of those plants, which are common to the 

 Galapagos and the adjacent continent, have all — as Sir 

 Joseph Hooker states — some special means of dispersal, is 

 equally intelligible. The reason why the Galapagos pos- 

 sess four times as many peculiar species of plants as the 

 Azores is clearly a result of the less constant introduction 

 of seeds, owing to the absence of storms; the greater 

 antiquity of the group, allowing more time for specifics 

 change ; and the influence of cold epochs and of alterations 

 of sea and land, in bringing somewhat different sets of 

 plants at different times within the influence of such 

 modified winds and currents as might convey them to the 

 islands. 



On the whole, then, we have no difficulty in explaining 

 the probable origin of the flora and fauna of the Galapagos, 

 by means of the illustrative facts and general principles 

 already adduced. 



u 2 



