ON THE MEALY LINNET. 455 



side the water, cannot be adduced as satisfactorily conclusive evidence of its 

 identity with the European bird. 



The two counter-ranged Bitterns, which are considerably the most unlike of 

 the several races thus posited, were regarded as mutual varieties by Dr. Latham ; 

 but are now, together with the six following, independently acknowledged, I 

 believe without a single dissentient. Some difference of opinion still exists as 

 to the establishment of Egretta leuca as distinct from E. alba, but the majority 

 of systematists certainly incline to the opinion that it is a separate species. The 

 Nightherons alone offer no difference of plumage ; and be it remarked that the 

 dissimilarity in this respect is but very inconsiderable in any of the foregoing 

 races, with the exception of the Bitterns ; that of structure being still less, and 

 the disparity of size trivial in some. The Nightheron of America, however, is 

 described by Wilson to measure "two feet four inches in length," and by 

 Nuttall " twenty-eight inches or upwards ;" whereas that of Europe, according 

 to Montagu, is only " twenty inches," and " twenty-one" as given by Mr. Jenyns. 

 Analogy with all the rest of the tribe would alone lead to the supposition that 

 these two races were distinct, even were not the above diversity so considerable. 

 Audubon indeed asserts that the American bird is subject to vary much in size ; 

 but I have repeatedly seen, in the London markets, a dozen or upwards of the 

 European race together, and could never discern any extraordinary inequality 

 among them. It will be necessary, however, to recur to this particular, which is 

 far from being unexplainable. 



Let us, in turn, consider all the differential characters upon which systematists 

 proceed to distinguish species ; and which, in dead specimens, may be reduced to 

 three, — structure, size, and colour. In living birds, the notes, nidification, eggs, 

 and general habits, may likewise be taken into consideration ; though perhaps 

 merely as adjuncts to the former. 



In the genus Tyrrhula, then, we have two races, the common European, and the 

 Japanese, which exactly resemble each other in size and structure, but differ slightly 

 (though perpetually) in colour ; also two European races, inhabiting the same 

 locality, which differ constantly and considerably in size, but in no other particu- 

 lar ; and the only invariable distinction prevailing between the African Elanus 

 melanopterus and American E. dispar, consists in the structure of the tail, the 

 outer feather of which is in the former rather the longest, and more than half an 

 inch shorter than the next in the latter. 



In three of the four cognizable races of Crossbill, the plumage is absolutely 

 alike ; their only differences being those of size and comparative strength of con- 

 formation. Mr. MacGillivray has consequently brought them together as a 

 single species, having noticed (what, I believe, is pretty generally known) that 

 aged or at least old specimens of each successively less robust of these races are 



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