and Nature of Specific Distinctions. 509 



is a sort of clustering of species (if I may be allowed the 

 phrase) about the centre of radiation. In v4'rdea, and C6r- 

 vus particularly, the central species become extremely dif- 

 ficult of determination ; if, indeed, in some instances, the 

 proximity is not even too close for detection. How nearly do 

 some of the typical crows resemble ! Upon the most scru- 

 pulous and minute comparison, C. L. Bonaparte was unable 

 to discern the least difference between specimens of the^Eu- 

 ropean Corvus Corone and the common crow of America; 

 and he consequently infers their identity : yet who that 

 attentively peruses the various descriptions of the latter, that 

 considers well its marked gregarious habits, and the diversity 

 of its note from that of our crow, can for a moment coincide 

 with him in opinion ? Look, again, to the raven, that for- 

 merly was considered a bird of universal distribution, as was 

 also the snipe. First, the African species must be detached, 

 as Le Vaillant's description of it should long ago have indi- 

 cated ; for we find that, independently of the differences in 

 the bill, and certain particulars connected with its plumage, 

 the proportionate size of the sexes is the reverse of that of 

 the European species, as Le Vaillant himself ascertained and 

 published. Then the beautifully glossed raven of the Brazils 

 is obviously distinct ; also the raven of the South Sea Islands, 

 and, there is reason to believe, that of India. And what if 

 these can be proved to be separate species, by fixed and 

 constant structural distinctions; do they not show how nearly 

 species may resemble, and point to the almost inevitable con- 

 clusion, that, in some instances, there may possibly be no 

 means whatever of knowing them apart ? 



How vastly important is this consideration when we con- 

 template the natural productions of America ! Many years 

 have now elapsed since the genius of Buffon suggested the 

 capital proposition, that there is no absolute specific identity 

 between any organism of the Eastern and Western continents, 

 with the exception of those which inhabit very far to the 

 north. All subsequent investigation has gone to prove the 

 force and acumen of this sterling remark; and the number 

 of species (exclusive of evident stragglers) supposed to be 

 common to the two continents has been gradually dimi- 

 nishing, on more careful and exact comparison from that 

 time to the present. In fact, I think we may now fairly ven- 

 ture to assume, putting aside stragglers, that those species 

 alone are satisfactorily identical in the two continents which 

 are distributed over the whole north of Asia, and may be 

 looked for on the north-western coast of America. Very lately, 

 the American scaup (pochard) was found, on comparison, 



pp 3 



