312 GEOGRAPHICAL DISTRIBUTION 
should. He took up the branch of the subject with which he 
was best acquainted, and pointed out and defined the Regions 
of the globe in conformity with the various aspects of ornithic 
life as known to him. But herein there was at once a great difli- 
culty to be met. Birds constituting the most vagrant Class of 
animals in existence, it was necessary for him to eliminate from 
consideration those groups of them, be they large or small, which 
are of more or less universal occurrence,! and to ground his results 
on what was at that time commonly known as the Order Jnsessores, 
comprehending those birds that are now generally differentiated as 
the groups or Orders, Passeres, Picariz, and Psittaci. 
On this basis, then, Mr. Sclater, after dwelling on the great 
distinction he thought observable between the Fauna of the Old 
World and of the New, was enabled to set forth that the surface of 
the globe exhibited siz great Regions, each in a marked manner 
differing from all the rest, though the difference was not always 
equally important. These Regions he termed respectively the 
Palxarctic, Ethiopian, Indian, Australian, Nearctic, and Neotropical— 
names which, so far as may be possible, it is convenient to preserve— 
and proof that the method he followed was the true one is afforded 
by the fact that these Regions have met with very general acceptance 
at the hands of those who study other groups of animals.” Without, 
1 Not but that even in the most widely-spread groups are contained others— 
subfamilies, genera, or species—strictly limited to certain localities. Some of 
them will be noticed further on. 
? This is a thing on which few writers seem to have dwelt sufficiently. What- 
ever be the causes, and it would be out of place here to discuss them, it must be 
admitted that what may be taken as a ‘‘law” of Geographical Distribution for 
one group of beings is not necessarily applicable to other groups. Botanists 
have shewn no disposition to accept the territorial divisions of their zoological 
brethren. It seems difficult to defend the position so often assumed that the 
boundaries set up for one group of animals are true for another, or still less that 
they are universally true. This fact has indeed had to be recognized in the case 
of some marine forims—for instance, Fishes, which, it is confessed, cannot be made 
subject to the limitations of terrestrial forms (cf. Giinther, Introduction to the 
Study of Fishes, pp. 259, 260), though Dr. Gill (Ann. and Mag. Nat. Hist. ser. 4, 
Xv. pp. 254, 255) recognizes for this Class what are practically the same divisions 
as those of Prof. Huxley—New Zealand, however, being placed with Australia. 
As regards the Land-Mollusks, malacologists demur to the geueral principles of 
Distribution which students of most Classes of Vertebrates accept, while even 
among Vertebrates themselves, and excluding Fishes, what is the best division 
of the Earth’s surface into Regions, Subregions, Provinces and so on, for Birds 
may not be the best for Mammals, Reptiles, or Amphibians. It would appear 
preferable to consider the case of each of these Classes on its own merits, and 
thus in what follows the territorial divisions adopted are in accordance with 
what it is supposed we know or seem to know of the Class Aves, and it may 
even be open to question whether the best division for one Subclass or Order of 
Birds is the best for another. 
