170 
ON THE GEOGRAPHICAL DISTRIBUTION OF BIRDS. 
series,” or the cotemporaneous habitants of diverse regions, Mr. Blyth regarded 
the respective distribution of types of form as strictly analogous; and contended 
that neither in the one case nor in the other was it possible to deduce universal 
laws, though of course it was highly necessary for the naturalist to possess a 
general knowledge of the vast accumulation of facts that had been elicited on 
the subject, if only that he might be effectually guarded against any delusory 
hypothesis, which a too hasty or insufficiently extensive generalization might 
otherwise lead him to fall into. A number of instances were then brought for¬ 
ward of types peculiar to certain eras, just as, at the present time, we find that 
others are confined to particular regions ; the location of which latter, however, 
was shown in some instances to be of comparatively recent date, species framed 
upon them having formerly been diffused over a more extensive area; while in 
other instances it would seem that the geographical limitation has remained the 
same from a very remote period, if not from the time of their original introduc¬ 
tion, of which the Kangaroos of Australia, and Lamas of South America, afforded 
illustrative examples. Cases were also adduced of groups of species, modified 
upon particular types of structure, to perform an especial office in the economy of 
Nature, which office, at another period of the earth’s history, appears to have 
been fulfilled by other groups, modified upon very different types of structure ; 
precisely as, at the present time, the Humming-birds, which are peculiar to 
America, are represented, in the tropical and southern regions of the old Continent 
and its islands, by analogous groups of nectar-feeding birds, of which the 
rudimental anatomy is widely dissimilar. It was thus that the Cetacea , though 
possessing all the essential characters of Mammalians, are modified to pass their 
lives after the manner of fishes: on the same principle, again, that corresponding 
groups in the different classes are observed, the part allotted to which in the 
grand scheme of the universe is absolutely the same. 
Mr. Blyth then proceeded to explain the important difference subsisting 
between what he designated the rudimentary and adaptive , or the intrinsical, as 
opposed to the superficial, characters of organized races; the former of which he 
affirmed to imply affinity, or physiological proximity, the latter merely what is 
understood by the term analogy. He decidedly opposed the popular theory of 
universal gradation (which supposes a concatenation of intermediate races, in 
which the rudimentary characters of distinct types are blended), however 
outward appearances might sometimes favour such a notion: the Rain-fowl 
(Scythrops) of New Holland, for instance, had been deemed a connecting link 
between the Toucans and the Cuckoos; but the Toucans and Cuckoos differ 
materially in the form of the skeleton, and in other details of their anatomy ; 
and Scythrops , Mr. Blytii asserted, is in every essential particular a true Cuckoo, 
with merely a larger bill than usual, this very superficial character constituting 
