CHAP. XIII.] 
THE AUSTRALIAN REGION. 
401 
and Steamer Back) are probably cases of abortion of use- 
less organs, and that the common ancestors of the various 
forms of Struthiones may have been capable of a moderate 
degree of flight ; or they may have originated in the northern 
hemisphere, as already explained in Chap. XI. p. 287. The exis- 
tence of two, if not three, distinct families of these birds in New 
Zealand, proves that the original type was here isolated at a 
very early date, and being wholly free from the competition of 
mammalia, became more differentiated than elsewhere. The 
Hatteria is probably coeval with these early forms, and is the 
only relic of a whole order of reptiles, which once perhaps 
ranged far over the globe. 
Still less does any other form of animal inhabiting New Zea- 
land, require a land connection with distant countries to account 
for its presence. With the example before us of the Bermudas 
and Azores, to which a great variety of birds fly annually over vast 
distances, and even of the recent arrival of new birds in New 
Zealand and Chatham Island, we may be sure that the ancestors 
of every New Zealand bird could easily have reached its shores 
during the countless ages which elapsed while the Dinomis and 
Apteryx were developing. The wonderful range of some of the 
existing species of lizards and fresh-water fish, as already given, 
proves that they too possess means of dispersal which have 
sufficed to spread them, within a comparatively recent period, 
over countries separated by thousands of miles of ocean; and the 
fact that a group like the snakes, so widely distributed and for 
which the climate of New Zealand is so well adapted, does not 
exist there, is an additional proof that land connection had nothing 
to do with the introduction of the existing fauna. We have 
already (p. 398), discussed in some detail the various modes in 
which the dispersal of animals in the southern hemisphere has 
been effected ; and in accordance with the principles there estab- 
lished, we conclude, that the New Zealand fauna, living and 
extinct, demonstrates the existence of an extensive tract of land 
in the vicinity of Australia, Polynesia, and the Antarctic con- 
tinent, without haviDg been once actually connected with either 
of these countries, since the period when mammalia had peopled 
