234 



ISLAND LIFE. 



[part II. 



direct and simple, and even when more complex are far easier to 

 comprehend than those of continents ; and they exhibit besides 

 certain influences on the forms of life and certain peculiarities of 

 distribution which continents do not present, and whose study 

 offers many points of interest. 



In islands we have the facts of distribution often presented 

 to us in their simplest forms, along with others which become 

 gradually more and more complex ; and we are therefore able to 

 proceed step by step in the solution of the problems they present. 

 But as in studying these problems we have necessarily to take 

 into account the relations of the insular and continental faunas, 

 we also get some knowledge of the latter, and acquire besides so 

 much command over the general principles which underlie all 

 problems of distribution, that it is not too much to say that when 

 we have mastered the difficulties presented by the peculiarities 

 of island life we shall find it comparatively easy to deal with the 

 more complex and less clearly defined problems of continental 

 distribution. 



Classification of Islands luith reference to Disti-ihution, — Islands 

 have had two distinct modes of origin ; they have either been 

 separated from continents of which they are but detached frag- 

 ments, or they have originated in the ocean and have never 

 formed part of a continent or any large mass of land. This 

 difference of origin is fundamental, and leads to a most 

 important difference in their animal inhabitants ; and we 

 may therefore first distinguish the two classes — oceanic and 

 continental islands. 



Mr. Darwin appears to have been the first writer who called 

 attention to the number and importance, both from a geological 

 and biological point of view, of oceanic islands. He showed that 

 with very few exceptions all the remoter islands of the great 

 oceans were of volcanic or coralline formation, and that none 

 of them contained indigenous mammalia or amphibia. He also 

 showed the connection of these two phenomena, and maintained 

 that none of the islands so characterised had ever formed part of 

 a continent. This was quite opposed to the opinions of the 

 scientific men of the day, who almost all held the idea of 

 continental extensions, and of oceanic islands being their 



