Chap. XIII."| INHABITANTS OF OCEANIC ISLANDS. 34D 



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 larva?, perhaps attached 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 

 different orders of insects inhabiting Madeira present nearly paralle" 



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. 

 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 separated from Australia by a profoundly 

 deep sea ; from its geological character and the direction of its 

 mountain-ranges, the Eev. W. B. Clarke has lately maintained 

 that this island, as well as New Caledonia, should be consideied 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 elsewhere. 

 All such differences in number, and the absence of certain whole 

 groups of animals and plants, are generally accounted for by sup- 

 posed differences in the physical conditions of the islands ; but this 

 explanation is not a little doubtful. Facility of immigration 

 seems to have been fully as important as the nature of the con- 

 ditions. 



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 manifest 

 than that hooks serve for the transportal of seeds in the wool 

 or fur of quadrupeds. But a hooked seed might be carried to 

 an island by other means ; and the plant then becoming modified 

 would form an endemic species, still retaining its hooks, which, 

 would form a useless appendage like the shrivelled wings under: 



