434 ORIGIN OF SPECIES 



birds are blown to Madeira; this island is inhabited by gcf 

 kinds, of which one alone is peculiar, though very closely 

 related to a European form ; and three or four other species 

 are confined to this island and to the Canaries. So that the 

 Islands of Bermuda and Madeira have been stocked from 

 the neighbouring continents with birds, which for long ages 

 have there struggled together, and have become mutually 

 co-adapted. Hence when settled in their new homes, each 

 kind will have been kept by the others to its proper place 

 and habits, and will consequently have been but little liable 

 to modification. Any tendency to modification will also have 

 been checked by intercrossing with the unmodified immi- 

 grants, often arriving from the mother-country. Madeira 

 again is inhabited by a wonderful number of peculiar land- 

 shells, whereas not one species of sea-shell is peculiar to its 

 shores; now, though we do not know how sea-shells are dis- 

 persed, yet we can see that their eggs or larvae, perhaps at- 

 tached to seaweed or floating timber, or to the feet of wading- 

 birds, might be transported across three or four hundred 

 miles of open sea far more easily than land-shells. The dif- 

 ferent orders of insects inhabiting Madeira present nearly 

 parallel cases. 



Oceanic islands are sometimes deficient in animals of cer- 

 tain whole classes, and their places are occupied by other 

 classes; thus in the Galapagos Islands reptiles, and in New 

 Zealand gigantic wingless birds, take, or recently took, the 

 place of mammals. Although New Zealand is here spoken 

 of as an oceanic island, it is in some degree doubtful whether 

 it should be so ranked; it is of large size, and is not sep- 

 arated from Australia by a profoundly deep sea; from its 

 geological character and the direction of its mountain-ranges, 

 the Rev. W. B. Clarke has lately maintained that this island, 

 as well as New Caledonia, should be considered as appur- 

 tenances of Australia. Turning to plants. Dr. Hooker has 

 shown that in the Galapagos Islands the proportional num- 

 bers of the dififerent orders are very different from what they 

 are elsewhere. All such differences in number, and the ab- 

 sence of certain whole groups of animals and plants, are gen- 

 erally accounted for by supposed differences in the physical 

 conditions of the islands; but this explanation is not a little 



