ON THE GEOGRAPHICAL DISTRIBUTION OF BIRDS. 
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its sole resemblance to the group of Toucans. In Nature, Mr. B. contended, we 
are presented with a succession of mutually distinct groups, rather than a con¬ 
tinuous series; with successively subordinate types of form, of every degree of 
value and of mutual affinity, on each of which may be framed an indefinite 
number of species, variously modified to suit any particular mode of life; the 
adaptive characters, however, consequent on such modification by no means 
affecting their intrinsical or physiological systematic relations. He was of opinion 
that the most approximate modifications of distinct types are not more nearly 
related by affinity , than are the more characteristic representatives of the same ; 
while, on the other hand, the most dissimilar modifications of the same possessed 
a higher degree of mutual affinity than either could have for any outwardly 
resembling species modified upon any other type. The group of Raptorial birds 
was cited in illustration, as comprising two principal subordinate types, distin¬ 
guished constantly by strongly marked differences in the structure of the skeleton 
and digestive organs ; and not the slightest trace of a gradation, or transition, in 
these rudimentary characters was stated to be observable, either in the most 
Owl-like Hawks or the most Hawk-like Owls, however in their superficial or 
merely adaptive characters they may reciprocally approximate. In like manner, 
to descend another grade, the Osprey was represented as being organized on a 
distinct minor type to that on which the rest of the European Falconidce are 
alike framed; and although it had been customary to regard the peculiarities of 
that genus as simply adaptive , yet it remained to be shewn, that any gradation 
towards those peculiarities is exhibited; for the Ernes, or Sea-eagles ( Haliceetus ), 
which subsist to a considerable extent on similar food, were described to be as 
widely separated in their internal structure from the Ospreys, as are the Hawks 
and Falcons. Pluck forth a single feather even, it was added, from an Osprey, 
and a corresponding one from an Erne, and their comparative structure will be 
found to corroborate strongly what has just been advanced. 
It was the especial province of the zoologist to distinguish, in every instance, 
the intrinsical from the simply adaptive characters of animals; to disentangle 
and discriminate affinity from analogy; to cease confounding those superficial 
resemblances which still induced the vulgar to style the Whale a fish, with those 
far more important and rudimentary characters on which the true station of that 
animal had been determined by naturalists. In Ornithology, Mr. Blyth re¬ 
gretted, too little attention had been paid to those more essential distinctions on 
which only a sound and permanent classification can be founded; and it was 
this that rendered it necessary for him to digress to enter into the foregoing' 
details, on the present occasion, in order to explain what he meant by asserting 
that particular types of form were represented only in certain regions, or during 
especial periods of time : otherwise, it was added, the statement that the Toucans 
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