62 



GENERAL ORNITHOLOGY. 



dosely agreeing with one another in the peculiar sum of their physical characters. In compar- 

 ison with other classes of Vertehrates, all hirds are mucli 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 liumming-bird and an ostrich, for example, is not greater 

 in degree tlian that subsisting between the members of some of the orders of Reptiles ; whence 

 some hold, with reason, that Birds should not form a class Aves, but an order, or at most a sub- 

 class, of Sauropsida, and so be compared not with a class Reptilia collectively, but with other 

 Sauropsidan orders, such as Chelonia (tintles), Sauria (lizards), Ophidia (serpents), etc. The 

 practical convenience of starting with a ''class" Aves, 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 

 they 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 has come to be, any more than 

 that Birds have been evolved from any such Reptiles as those of the present day. It is one 

 of the popular misunderstandings of the Theory of Evolution, to imagine that all the lower 

 forms of animals are in the genetic line of development of the higher forms ; that man, for 

 example, was once a gorilla or a chimpanzee — actually such an ipe. The theory simply 

 requires all forms of life to be developed from some antecedent form, presumably, and in most 



cases certainly, lower in the scale of or- 

 ganization. Thus man and the gorilla 

 are both descendants of some common 

 progenitor, more or less unlike either of 

 these existing creatures. All maiumiils 

 are similarly the modified descendants of 

 some more primitive stock, from which 

 stock sprang also all Sauropsida, medi- 

 ately or immediately ; therefore, a Mam- 

 mal is not a modified Bird, though higher 

 in the scale ; and, though a Bird is a 

 modified Reptile, it is not a modification 

 of any such snake or lizard as now ex- 

 ists. The most bird -like reptiles known 

 are not the Pterodactyls, or Flying Rep- 

 tiles {Pterosaur ia^, as might be sup- 

 posed ; but of that remarkable order, the 

 Ornithoscelida, comprising the Dinosau- 

 rians, which "present a large series of 

 modifications intermediate in structure 

 between existing Reptilia and Aves," 

 and are therefore inferentially in the 

 direct ancestral line of modern Birds. 



Fig. 14. —Oldest known ornithological treatise, illus- 

 trating also the art of lithography in tbe Jurassic period, 

 engraved by ArchcBopteryx lithographica. From the original 

 slab in the British Museum ; after A. Newton, Ewy. BHt. 



Geologic Succession of Birds. — 



Birds have been ti-tced back in geologic 

 time to Cretaceous and Jurassic epocli^ 

 of the Mesozoic or Mid-Life period of 

 the world's history. The earliest ornith ■ 



