Xii A MANUAL OF THE BIRDS OF AUSTRALIA. 



The complex persists in the fact that it is sometimes difficult to judge whether 

 a species, as it may show little distinction, should be referred to this or the 

 earlier migration, and this can only be determined by the relative antiquity 

 of the genus considered. This may be gauged to some extent by the distribu- 

 tion of the genus and its allies, and it is in connection with these studies that 

 genus lumping proves so misleading. We conclude that when this second 

 migration took place Australia was connected by land with New Guinea, 

 and Torres Straits had not been evolved. Since the division a third irruption 

 into Australia has taken place, and the procedure is still going on. This 

 irruption has never overrun the continent, but has either run down the east 

 coast or along the north coast into the north-west or both, and comprises 

 species still living unchanged in New Guinea. It has been suggested that at 

 one time a connection of Australia with the Northern Islands existed in the 

 north-west, quite distinct and separate from the Torresian connection. There 

 exist a few forms which seem to countenance this suggestion, as instance, 

 Eremiornis, isolated in the north-west and living on the Montebello Islands, 

 a form almost as peculiar as Atrichornis. To crystallise the above migrations 

 we may cite a concrete example. The ancestral Moorhen arrived in Australia 

 and penetrated into Tasmania ; retaining primitive features upon the separa- 

 tion of the latter country, the island form degenerated into a huge semi- flightless 

 big-footed bird ; the mainland one, through stress of environment, drought r 

 etc., was compelled to retain its flying powers and also its smaller size, but 

 still shows primitive appearance. In the north, alteration through necessity 

 proceeded, and then the more highly developed bird with the second immigration 

 proceeded to colonise Australia, and spread over the continent but not into 

 Tasmania. At the third immigration a new development, the Rufous-tailed 

 Moorhen, crossed Torres Straits and ranged along the north to the Northern 

 Territory and into North Queensland. This sequence can be traced in 

 connection with many other birds and is worthy of study. A few words 

 must be given in connection with the desert forms ; these are apparently 

 referable to the first immigration and have been evolved through environmental 

 stresses, sometimes so much that their relationship has become obscure, and 

 it is always possible that their ancestral relations have become extinct without 

 leaving any obvious descendants. It is possible that complete anatomical 

 and osteological examination would assist in tracing such to an acceptable 

 ancestry, and as a good example for investigation we suggest Peltohyas, the 

 Australian Dotterel. 



Though the arrangement in this work is limited to species it must not be 

 concluded that we minimise the value of the study of subspecies, but rather 

 we have allotted to them their full value, and we appreciate their worth in the 

 consideration of zoogeographical problems, especially such as are presented 

 by the numerous " islands " indicated on the Australian mainland. These 

 have been previously indicated by Mathews, so we will not deal with them 

 here, but simply call attention to their presence once again. The study of 

 subspecies is now being undertaken by Australian ornithologists, and it id 



