PROBLEMS OF DISTRIBUTION AND THEIR SOLUTION. 163 



to the facts of geological change for a solution of the difficulties in ques- 

 tion. If we suppose, firstly, that Himalayan species, driven southwards 

 by climatal or other changes, found a home in Java ; and, secondly, 

 that the separation of Java from the adjoining lands took place long 

 prior to the isolation of Borneo and Sumatra from the Malay penin- 

 sula, we may fully account at once for the persistence of Asiatic 

 animals in Java, and for its differences from Borneo on the one hand 

 and Sumatra on the other. In such an explanation, let us note, we 

 must likewise take the facts of organic variation, producing change 

 and modification of species, into account. The peculiarities of the 

 Philippine Islands, which were separated in their turn earlier than 

 Java from the mainland, can be accounted for on the same principle 

 of isolation, entailing a corresponding modification of the life of any 

 area. 



No less interesting is the history of such islands as the Azores, 

 and Galapagos, which represent " oceanic" islands, never connected 

 with a continent or large land area ; or the history of such isolated 

 lands as the British Islands, which are clearly of " continental " 

 origin, and which once formed part of the larger land area to the 

 south and west : whilst such islands as Madagascar or New Zealand 

 present us with an instance of specialised land surfaces, whose con- 

 nection with continents is a thing of the very remote past. A 

 reference to each of these islands will serve to establish more firmly 

 and clearly in the mind the high importance of physical change as a 

 paramount condition in determining the distribution of life on the globe. 



The Azores and Galapagos islands are typically "oceanic." San 

 Miguel, in the Azores, is 900 miles from the coast of Portugal as the 

 nearest continental area ; whilst the Galapagos are about 600 miles 

 from the west coast of South America. In these islands we see 

 exemplified the characters of " oceanic " islands. They are volcanic 

 in nature, and represent rock masses upheaved from the sea-depths. 

 As in oceanic islands, at large, there are no native quadrupeds, and 

 none of the frog or toad class {Amphibia}. In the Azores there is 

 not a single native, terrestrial vertebrate animal no snake or lizard 

 being found in addition to the already specified omissions; and no 

 fresh-water fishes exist. The rabbits, weasels, rats, and mice of the 

 Azores, and a single lizard, occurring in Madeira and Teneriffe like- 

 wise, are all importations ; and of the eels and gold-fish in the lakes 

 of the Azores, the same opinion may be expressed. Birds, land- 

 shells, and insects constitute the animal population of these islands. 

 Of 53 species of birds, 31 are waders or swimmers; and whilst 20 

 aquatic birds are residents, 18 of the land birds are permanent 

 tenants. With three exceptions, the 18 land birds, however (including 

 the quail, robin, barn-owl, starling, wood-pigeon, &c.), are common 

 in Europe and North Africa; the exceptions being the Atlantic 



M 2 



