386 INHABITANTS OF OCEANIC ISLANDS. 



arrival of unmodified immigrants from the mother-country, 

 with which the insular forms have intercrossed. It should 

 be borne in mind that the offspring of such crosses would 

 certainly gain in vigor ; so that even an occasional cross 

 would produce more effect than might have been anticipated. 

 I will give a few illustrations of the foregoing remarks : 

 in the Galapagos Islands there are twenty-six land birds ; of 

 these, twenty-one (or perhaps twenty-three) are peculiar, 

 whereas of the eleven marine birds only two are peculiar ; 

 and it is obvious that marine birds could arrive at those 

 islands much more easily and frequently than land birds. 

 Bermuda, on the other hand, which lies 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' admirable account of Bermuda, that 

 very many North American birds occasionally or even 

 frequently visit this island. Almost every year, as I am 

 informed by Mr. E. Harcourt, many European and African 

 birds are blown to Madeira; 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 modifica- 

 tion 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 



