INTRODUCTION. xi 
Victorian fauna is divisible into three sections—a northern, southern, and 
western desert one. 
Consequently Victoria is a confusing term when cited as the locality of 
any bird, and this refers to most other State names, though not so well marked 
in so circumscribed an area. The most famed endemic Australian birds, such 
as the Emu and Lyre Bird, are equalled in zoogeographic interest by less 
well-known forms which are too numerous even to mention here. Each 
provides an essay in itself as to its distribution, but it may here be asserted 
that all are confined to the southern part of Australia, both east and west. 
At the present time some show discontinuous range through the intervention 
of the great central desert. Some, apparently definitely restricted and evolved 
in this southern area, have again spread northwards and repopulated the 
areas from which their ancestors ranged southwards. At the same time 
the succeeding fauna has extended its limits and penetrated into Australia 
even to the southernmost limits, but scarcely ever reaching Tasmania. It is 
this complex which makes the study so interesting, as the facts are so obvious 
that these succeeding migrations can almost be defined with unfailing accuracy. 
However, we will suggest these movements, without dealing in great detail, 
thus : Paleontologically, we have not the data to assert a definite period, 
but we can fix an early migration from the north which overran Australia 
before the severance of the Bassian Isthmus and whose members quickly 
developed in a degenerate manner through lack of inimical opposition. The 
separation of Tasmania took place after degeneration had set in, so that the 
island forms were left as isolated unprogressives. On the mainland, changing 
conditions compelled a certain amount of competition, and we find the con- 
temporaries of the island species a little more advanced on the mainland. 
Some of them even, adapting themselves as the situations demanded, progressed 
so that they could not only defend themselves but take the offensive, and 
these, being barred from any advance southward, attempted a northward 
dispersal. These constitute the bulk of the Australian Ornis and include 
the majority of the endemic genera and species. From the observed data 
we conclude that after the division of Bass Straits another immigration from 
the north took place and this also succeeded in overrunning Australia, but 
did not cross the Straits into Tasmania. It is probable that the competi- 
tion between these two elements—the invaders and the settlers—resulted in 
the extermination of many of the weaker forms of the latter, a few resisting 
and being now recognised in such a survival as Atrichornis. The stronger 
settlers, of course, continued their progress accumulatively under the stress 
of the stronger newcomers in order to retain their places. The new 
immigrants in their turn soon accustomed themselves to the environment 
and became adapted to the lack of great stress, and a few of these again evolved 
the role of pioneer and perforce had to retrace their ancestors’ steps into the 
north. In these attempts probably many more failed than succeeded, and 
we have only record of the successes. This migration can be seen throughout 
Australia in the form of differentiated species of prevailing northern genera. 
