INHABITANTS OF OCEANIG ISLANDS. 411 



Although in oceanic islands the species are few in 

 number, the proportion of endemic kinds {i. e. those 

 found nowhere else in the world) is often extremely large. 

 If we compare, for instance, the number of endemic land- 

 shells in Madeira, or of endemic birds in the Galapagos 

 Archipelago, with the number found on any continent, 

 and then compare the area of the island with that of the 

 continent, we shall see that this is true. This fact might 

 have been theoretically expected, for, as already explained, 

 species occasionally arriving, after long intervals of time in 

 the new and isolated district, and having to compete with 

 new associates, would be eminently liable to modification, 

 and would often produce groups of modified descendants. 

 But it by no means follows that, because in an island 

 nearly all the species of one class are peculiar, those of 

 another class, or of another section of the same class, are 

 peculiar; and this difference seems to depend partly on the 

 species which are not modified having immigrated in a 

 body, so that their mutual relations have not been much 

 disturbed; and partly on the frequent 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 pro- 

 duce more effect than might have been anticipated. I will 

 give a few illnstrations 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 these islands 

 much more easily and frequently than land birds. Ber- 

 muda, on the other hand, which lies at about the same 

 distance from ISTorth 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. B. V. 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 



