ON THE GEOGRAPHICAL DISTRIBUTION OF BIRDS. 
173 
or rather, according to the range of a particular climate. Several European birds 
are thus met with at a particular altitude on the mountains of India, and thence 
onward to China and Japan; and, indeed, the European types of form are so 
prevalent in those regions, though gradually mingling, of course, on the southern 
confines, with others proper to the adjacent countries, that there appears to be no 
reason why the entire circuit, northward of about the 30° parallel, might not be 
included as a single zoological region, on the same principle that North America 
and Europe have been so ranged. We know but little, at present, of the animal 
inhabitants of the extreme eastern portion of Asia, though it is probable that 
their general character does not differ materially from that of the races which 
inhabit the opposite coast of America; in some instances, indeed, we find North- 
American forms extending even to the mountains of India; as is exemplified by 
the existence of a Blue Jay (pertaining to the division Cyanurus , Swainson) 
in the Himmalayas, all the other species of which group are exclusively natives 
of North America. 
Attention was next called to the Ornithology of the southern hemisphere, 
which was stated to be considerably more tropical in its general character than 
that of corresponding latitudes of the northern : this was especially shewn by 
the much greater proportion of frugivorous and nectar-feeding species, among 
which the Parrot family bore a conspicuous station. Several forms, as the Pen¬ 
guins, were indicated as peculiar to that hemisphere; and instances of congenerous 
species adduced as inhabiting South Africa and New Holland; while that extra¬ 
ordinary and gigantic Dentirostral bird, the Australian Menura , found its nearest 
systemati c relatives in the Megapodii , from the neighbourhood of Cape Horn. 
Of the intertropical genera, comparatively few were represented in both the Old 
world and the New; and many were confined to rather circumscribed localities. 
The Trogons, of which several species occurred both in South America and in 
the Oriental Isles, possessed, in each locality’', certain discriminating characters, 
which were curiously combined in the only species known to inhabit Africa. It 
was affirmed that a multitudinous host of diversified facts might be enumerated, 
which, however, would not admit of being generalized into a definite system; 
and Mr„ Blyth accordingly proceeded to consider the laws which tend to regulate 
and limit the dispersion of particular species. He dwelt on the minute adapta¬ 
tion of each to its indigenous locality, removed from which it was little else than 
a disjointed fragment, and this in proportion to the exactness with which it was 
modified for any peculiar mode of obtaining subsistence; and he insisted much on 
the efficacy of what he denominated the u localizing principle,” that which impels 
a Pigeon homeward from a distance of many hundred miles, a Bee towards its 
hive, and by means of which migratory species of birds revisit, both in winter 
and summer, the exact same haunts which they had formerly occupied; of which 
