The geographical distribution of animals, with a study of the relations ...

and176 ZOOLOGICAL GEOGRAPHY. [part hi.agencies in the limitation of their range. Even among theaerial bats, however, only one family-—the Vespertilionidae— istruly cosmopolitan, the others having a more or less restrictedrange.Neither are the Cetacea necessarily cosmopolitan, most ofthe families being restricted either to warm or to cold seas ; butone family, the dolphins (Delphinidae), is truly so. This orderhowever will not require further notice, as, being exclusivelymarine the groups do not enter into any of our terrestrialregions. The only other family of mammals that may be consideredto be cosmopolitan, is the Muridae (rats .mice) : yetthese are not entirely so, since none are known to be trulyindigenous in any part of the Australian region except Australiaitself.In the class of Birds, a number of families are cosmopolites,if we reckon as such all which are found in each region andsub-region ;but several of these are so abundant in some parts,while they are so sparingly represented in others, that theycannot fairly be considered so. We shall confine that termtherefore, to such as, there is reason to believe, inhabit everyimportant sub-division of each region. Such are, among thePasserine birds the crows (Corvidae), and swallows (Hiruudinidae);.among the Picariae the kingfishers (Alcedinidae) ; amongother Land birds the pigeons (Columbidae), grouse and partridges(Tetraonidae), hawks (Falconidae), and owls (Strigidae) ; amongthe Waders the rails (Kallidae), snipes (Scolopacidae), plovers(Charadriadae), and herons (Ardeidae) ;and among the Swimmersthe ducks (Anatidae), gulls (Laridae), petrels (Procellariidae),pelicans (Pelecanidae), and grebes (Podicipidae).In the class of Reptiles there are few absolutely cosmopolitanfamilies, owing to the scarcity of members of this group in someinsular sub-regions, such as New Zealand and the Pacific Islands.Those which are most nearly so are the Colubridae among snakes,and the Scincidae among lizards.There isno cosmopolitan family of Amphibia, the true frogs(Eanidae) being the most widely distributed.Neither is any family of Freshwater Fishes cosmopolitan,the Siluridae, which have the widest range, being confined