408 ISLAND LIFE 



have enabled it to preserve an unusual number of Hima- 

 layan and Malayan forms. Japan, almost equally isolated 

 towards tlie south, and having a much greater variety of 

 climate as well as a much larger area, possesses about an 

 equal number of mammalia with Formosa, and an even 

 larger proportion of peculiar species. Its birds, however, 

 though more numerous are less peculiar ; and this is 

 probably due to the large number of species which migrate 

 northwards in summer, and find it easy to enter Japan 

 through the Kurile Isles or Saghalien.^ Japan too, is 

 largely peopled by those northern types which have an 

 unusually wide range, and which, being almost all migratory, 

 are accustomed to cross over seas of moderate extent. 

 The regular or occasional influx of these species prevents 

 the formation of special insular races, such as are almost 

 always produced when a portion of the population of a 

 species remains for a considerable time completely isolated. 

 We thus have explained the curious fact, that while the 

 mammalia of the two islands are almost equally peculiar, 

 (those of Japan being njost so in the present state of our 

 knowledge), the birds of Formosa show a far greater 

 number of peculiar species than those of Japan. 



General Remarks on Recent Continental Islands. — We have 

 now briefly sketched the zoological peculiarities of an 

 illustrative series of recent continental islands, commencing 

 with one of the most recent — Great Britain — in which the 

 process of formation of peculiar species has only just 

 commenced, and terminating with Formosa, probably one 

 of the most ancient of the series, and which accord- 

 ingly presents us with a very large proportion of peculiar 

 species, not only in its mammalia, which have no means of 

 crossing the wide strait which separates it from the mainland, 

 but also in its birds, many of which are quite able to cross 

 over. 



Here, too, we obtain a glimpse of the way in which 



^ Captain Blakistoii lias shown that the northern island — Yezo — is much 

 more temperate and less peculiar in its zoology than the central and southern 

 islands. This is no doubt deijendent cliiefly on the considerable change of 

 climate that occurs on passing the Tsu-garu strait. 



