GEOGRAPHICAL DISTRIBUTION 189 



at about the same distance from North America as the 

 Galapagos Islands do from South America, and which has 

 a very peculiar soil, does not possess a single endemic 

 land bird; and we know from Mr. J. M. Jones's admi- 

 rable account of Bermuda that very many North Ameri- 

 can birds occasionally or even frequently visit this island. 

 Almost every year, as I am informed by Mr. E. V. Har- 

 court, many European and African birds are blown to 

 Madeira; this island is inhabited by 99 kinds, of which 

 one alone is peculiar, though very closely related to a 

 European form; and three or four other species are con- 

 fined 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 won- 

 derful 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 or- 

 ders of insects inhabiting Madeira present nearly parallel 



CftSGS. 



Oceanic islands are sometimes deficient in animals 



