8 ANIMALS WITH RESTRICTED RANGE. [CH. t 



nowhere else in the world. The limitation of particular 

 species of humming-birds to particular peaks of the Andes, 

 and of snails to particular valleys, are other examples. 

 Francolinus Kirki of the island of Zanzibar is almost as 

 striking an instance of the same phenomenon. The Ven- 

 dace (Coreyonus vandesius) restricted to Loch Maben in 

 Dumfriesshire is an animal with a still more limited range, 

 and several other examples might be given, particularly 

 from the faunas of islands. The two extremes are natu- 

 rally connected by numerous intermediate stages, where an 

 animal has a more or less limited habitat. 



Cosmopolitan groups. 



There are comparatively few groups of terrestrial 

 animals which are truly cosmopolitan. As the groups 

 get smaller the number of those that are cosmopolitan 

 decreases. That is to say, there are more cosmopolitan 

 families than genera, and more genera that are cosmo- 

 politan than species. 



Mr Wallace enumerates in his work upon Geographical 

 Distribution no less than sixteen families of birds which 

 are really cosmopolites ; they are, Corvidcs (Crows) and 

 Hirundinidce (Swallows) among Passerines; Kingfishers 

 among Picariae ; among other land birds, Columbidce 

 (Doves), Tetraonidce (Grouse), Falconidce (Hawks), Stri- 

 gidce (Owls) ; among waders Rallidce (Rails), Scolopacidce 

 (Snipe), Charadrice (Plovers), Ardeidw (Herons); among 

 aquatic birds Anatidce (Ducks and Geese), Laridce (Gulls), 

 Procellaridce (Petrels), Pelecanidce (Pelicans) and Podici- 



