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=—~e eee 
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INTRODUCTION. XV 
Since, then, all attempts at a linear arrangement must be artificial, and 
the classification of families into orders is impossible in the present state 
of our knowledge, I have arranged the families in the old but, to a large 
extent, artificial sequence adopted by Cuvier, which has at least the prac 
tical value that it is well known, and thus obviates to a large extent the 
trouble of referenee to an index. I have been careful to point out under 
each family whether, in the opinion of the best informed naturalists, it is 
nearly connected or not with the families near which it is placed. 
There is no department of ornithology which has received more atten- 
tion of late years than that of 
GEOGRAPHICAL DISTRIBUTION ; 
and there is no subject more intimately connected with the discrimination 
of species and with the whole question of classification. The zoological 
divisions into which naturalists divide the world are not the same as those 
in common use among geographers. So far as these boundaries are deep- 
sea, they may be said to be practically the same. Where there are no 
changes of climate to make it imperative upon birds to migrate it is 
remarkable how seldom they use their powers of flight to wander far from 
home. Even the narrow channel of deep sea between Borneo and Celebes 
marks an important boundary in the geographical distribution of birds, 
whilst the shallow Mediterranean is of little significance. 
The land-boundaries of the zoological regions are climatic. The world 
is divided into six or seven zoological regions. 
The Palearctic Region contains the whole of the Old World north of the 
desert of Sahara in Africa and north of the Himalayas in Asia. 
The Nearctic Region contains the New World north of the tropics, 2. e. 
north of Mexico. 
The Ethiopian Region consists of Africa south of the great desert, and 
Southern Arabia. 
The Oriental Region consists of Asia south of the Himalayas, and the 
islands of the Malay archipelago as far east as Borneo. 
The Australian Region consists of the rest of the islands of the Pacific. 
The Circumpolar Region has the north pole for its centre, and extends 
to the Arctic circle in the Old World, and somewhat further south in the 
New; but many naturalists do not recognize this region as zoologically 
distinct. 
Perhaps the most interesting fact connected with these divisions is that 
in the tropical regions most birds vary much less than they do in the arctic. 
regions. If we eliminate the arctic genera, which are comparatively recent 
emigrants, we shall find that the tropical species are generally well defined ; 
they are obviously ancient residents who have well nigh exhausted the 
variations required to adapt them to their surroundings, which must have 
