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

chap, xni.] THE AUSTRALIAN REGION. 461and Steamer Duck) are probably cases of abortion of uselessorgans, and that the common ancestors of the variousforms of Struthiones may have been capable of a moderatedegree of flight ; or they may have originated in the northernhemisphere, as already explained in Chap. XI. p. 287.The existenceof two, if not three, distinct families of these birds in NewZealand, proves that the original type was here isolated at avery early date, and being wholly free from the competition ofmammalia, became more differentiated than elsewhere. TheHatteria is probably coeval with these early forms, and is theonly relic of a whole order of reptiles, which once perhapsranged far over the globe.Still less does any other form of animal inhabiting New Zealand,require a land connection with distant countries to accountfor its presence. With the example before us of the Bermudasand Azores, to which a great variety of birds fly annually over vastdistances, and even of the recent arrival of new birds in NewZealand and Chatham Island, we may be sure that the ancestorsof every New Zealand bird could easily have reached itsshoresduring the countless ages which elapsed while the Dinornis andApteryx were developing. The wonderful range of some of theexisting species of lizards and fresh-water fish, asalready given,proves that they too possess means of dispersal which havesufficed to spread them, within a comparatively recent period,over countries separated by thousands of miles of ocean; and thefact that a group like the snakes, so widely distributed and forwhich the climate of New Zealand is so well adapted, does notexist there, is an additional proof that land connection had nothingto do with the introduction of the existing fauna. We havealready (p. 398), discussed in some detail the various modes inwhich the dispersal of animals in the southern hemisphere hasbeen effected ;and in accordance with the principles there established,we conclude, that the New Zealand fauna, living andextinct, demonstrates the existence of an extensive tractof landin the vicinity of Australia, Polynesia, and the Antarctic continent,without having been once actually connected with eitherof these countries, since the period when mammalia had peopled