Chap. XII. 
OCEANIC ISLANDS. 
391 
it should be remembered that the offspring of such 
crosses would almost certainly gain in vigour; so that 
even an occasional cross would produce more effect than 
might at first have been anticipated. To give a few 
examples: in the Galapagos Islands nearly every land- 
bird, but only two out of the eleven marine birds, are 
peculiar; and it is obvious that marine birds could 
arrive at these islands more easily 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 one endemic land-bird; 
and we know from Mr. J. M. Jones’s admirable account 
of Bermuda, that very many North American birds, 
during their great annual migrations, visit either periodi¬ 
cally or occasionally this island. Madeira does not 
possess one peculiar bird, and many European and 
African birds are almost every year blown there, as I 
am informed by Mr. E. V. Harcourt. So that these 
two islands of Bermuda and Madeira have been stocked 
by birds, which for long ages have struggled together 
in their former homes, and have become mutually 
adapted to each other; and when settled in their new 
homes, each kind will have been kept by the others to 
their proper places and habits, and will consequently 
have been little liable to modification. Any tendency 
to modification will, also, have been checked by inter¬ 
crossing with the unmodified immigrants from the 
mother-country. Madeira, again, is inhabited by a 
wonderful number of peculiar land-shells, whereas not 
one species of sea-shell is confined to its shores: now, 
though we do not know how sea-shells are dispersed, yet 
we can see that their eggs or larvse, perhaps attached 
to seaweed or floating timber, or to the feet of wading- 
birds, might be transported far more easily than land- 
