GEOGRAPHICAL DISTRIBUTION 357 



deira; this island is inhabited by ninety-nine 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 neighboring 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 immigrants, 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 dispersed, yet we can see that their 

 eggs or larvae, perhaps attached to sea-weed 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 different orders of insects inhabiting Madeira present 

 nearly parallel cases. 



Oceanic islands are sometimes deficient in animals of certain 

 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. Al- 

 though 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 separated 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 appurtenances of Australia. Turning to plants. Dr. Hooker has 

 shown that in the Galapagos Islands the proportional numbers 

 of the different orders are very different from what they are else- 

 where. All such differences in number, and the absence of certain 

 whole groups of animals and plants, are generally accounted for 

 by supposed differences in the physical conditions of the islands; 

 but this explanation is not a little doubtful. Facility of immigra- 

 tion seems to have been fully as important as the nature of the 

 conditions. 



Many remarkable little facts could be given with respect to the 

 inhabitants of oceanic islands. For instance, in certain islands 

 not tenanted by a single mammal, some of the endemic plants 

 have beautifully hooked seeds; yet few relations are more mani- 



