. Key to North American birds [microform] : containing a concise account of every species of living and fossil bird at present known from the continent north of the Mexican and United States boundary, inclusive of Greenland. Birds; Ornithology; Oiseaux; Ornithologie. 62 GENEBAL ORNITHOLOGY. closely agreeing with one another in the peculiar sum of their physical characters. In compar- ison with other classes of Vertchrates, nil birds are much alike; there is a less degree of difference among them than that found among the members of any of the other classes of Verte- brates : their likeness to
. Key to North American birds [microform] : containing a concise account of every species of living and fossil bird at present known from the continent north of the Mexican and United States boundary, inclusive of Greenland. Birds; Ornithology; Oiseaux; Ornithologie. 62 GENEBAL ORNITHOLOGY. closely agreeing with one another in the peculiar sum of their physical characters. In compar- ison with other classes of Vertchrates, nil birds are much alike; there is a less degree of difference among them than that found among the members of any of the other classes of Verte- brates : their likeness to each other being strong, and their kind of difference from any other Vertebrates being peculiar, makes them the ''highly specialized" class they are recognized to be. The structural difference between a humming-bird and an ostrich, for example, is not greater in degree than that subsisting between tlie members of some of tlie orders of Reptiles ; whence some hold, witli reason, that Birds sliould not form a class Aves, but an order, or at most a sub- class, of Sauropsida, and so be compared not with a class lleptilia collectively, but with other Sauroi)sidan orders, such as Chelonia (turtles), Sauria (lizards), Ophidia (serpents), etc. The pnictical convenience of starting witli a " class" .4i', however, is so great, that such classificatory value will probably long continue to be ascribed, as heretofore, to Birds collectively. I have spoken of Birds as a particular " side-issue " or lateral branch of the Vertebrate " tree of life " '< hence it is not to be supposed that they are in the direct line of genealogical descent. Though tliey stand as a group next below Mammals in the scale of evolution, it does not follow that Mammals were developed from any such (creature as a Bird lias come to be, any more than that Birds have been evtdved from any such Reptiles as those of the present day. It is ouv of the popular misunderstandings of the T
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbirds, bookyear1884
