^6 A HISTORY OF BIRDS 



also in Africa, India and the Malayan Region, the distribution of 

 which we propose to speak of presently. 



Such, in brief, are the main outlines of the Zoogeographical 

 Regions of the world. To have worked this out in fuller detail 

 a whole volume would be required, and those who desire to 

 acquaint themselves more fully with this subject should consult 

 the works of such exponents of the subject as Russel Wallace, 

 Sclater, Lydekker, Beddard, Heilprin, Sharpe and others. 



In the earlier part of this chapter a reference was made to 

 the phenomena of continuous and discontinuous distribution. 

 Let us return now to a more careful, if brief, consideration 

 thereof. The older writers held that similar forms occupying 

 isolated areas were to be regarded as independently created 

 forms, but this, in the light of modern biological science, cannot 

 be regarded as a tenable hypothesis. 



How, then, are we to explain the fact that certain families 

 and genera of birds are confined to certain well-defined areas 

 in Africa and South America, for example, on the one hand, 

 and to Africa, India, the Indo-Malay Peninsula and Australia 

 on the other ? 



This question has already been discussed by other writers 

 at various times, and many interpretations of the riddle have 

 been offered. Space forbids anything more than a bare outline 

 of the two most probable of the suggested explanations of this 

 matter. 



Briefly, according to one hypothesis, these forms, in common 

 with others of cosmopolitan range, originated in a great southern 

 land area, circumpolar in extent, which, extending northwards, 

 served during tertiary times to link together the several 

 Continents concerned in this discussion. For this Continent 

 Dr. H. O. Forbes — the originator of the hypothesis — suggested 

 the name "Antarctica". It apparently followed the 2,000 

 fathom line extending northwards by broad expansions to 

 join an old New Zealand continental island (including the 

 Antipodes, Macquaries, New Zealand and Chatham, Lord 

 Howe, Norfolk and the Kermadec and Fiji Islands) ; a second 

 to East Australia and Tasmania ; a third to the Mascarene and 

 adjacent islands ; perhaps one to South Africa and finally one 

 to South America. 



The Trogons, Parrots and Struthious birds were cited by 



