332 ISLAND LIFE part ii 



other in size, in antiquity, and in the richness of their 

 respective faunas, as well as in their distance from the 

 parent land and the facilities for intercommunication with 

 it ; and these diversities of conditions will manifest them- 

 selves in the greater or less amount of speciality of their 

 animal productions. 



This speciality, when it exists, may have been brought 

 about in two ways. A species or even a genus may on a 

 continent have had a very limited area of distribution, and 

 this area may be wholly or almost wholly contained in the 

 separated portion or island, to which it will henceforth bo 

 peculiar. Even when the area occupied by a species is 

 pretty equally divided at the time of separation between 

 the island and the continent, it may happen that it will 

 become extinct on the latter, while it may survive on the 

 former, because the limited number of individuals after 

 division may be unable to maintain themselves against the 

 severer competition or more contrasted climate of the 

 continent, while they may flourish under the more favour- 

 able insular conditions. On the other hand, when a 

 species continues to exist in both areas, it may on the 

 island be subjected to some modifications by the altered 

 conditions, and may thus come to present characters which 

 differentiate it from its continental allies and constitute it 

 a new species. We shall in the course of our survey meet 

 with cases illustrative of both these processes. 



The best examples of recent continental islands are 

 Great Britain and Ireland, Japan, Formosa, and the larger 

 Malay Islands, especially Borneo, Java, and Celebes ; and 

 as each of these presents special features of interest, we 

 will give a short outline of their zoology and past history 

 in relation to that of the continents from which they have 

 recently been separated, commencing with our own islands, 

 to which the present chapter will be devoted. 



Recent Physical Changes in the British Isles, — Great 

 Britain is perhaps the most typical example of a large and 

 recent continental island now to be found upon the globe. 

 It is joined to the Continent by a shallow bank which 

 extends from Denmark to the Bay of Biscay, the 100 

 fathom line from these extreme points receding from the 



