ON THE GEOGRAPHICAL DISTRIBUTION OF BIRDS. 171 



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 Toucani 



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