62 



GENERAL ORNITHOLOGY. 



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

 ison with other classes of Vertehrates, all birds are much alike ; there is a less degrei^ of 

 difference among them than that found among the members of any of the other classes of Verte- 

 brates ; their likeness to each otlier being strong, and thoir kind of difference from any other 

 Vertelirates being peculiar, makes them the "highly specialized" class they are recognized to 

 1)0. The structural difference between a humming-bird and an (jstricli, for example, is not greater 

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

 some liold, 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 or<lers, such as Chelonia (turtles), Sauria (lizards), Opliidia (serpents), etc. The 

 practical convenience of starting with a "class" ^ces, however, is so great, that suoli classificatory 

 value will probably long continue to be ascribed, as heretofore, to Birds conectively. 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 tlie direct line of genealogical descent. Though 

 they stand as a group nest below Mammals in the scale of evolution, it does not follow that 

 Mammals were developed from any such creature as a Biid 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 tliat all the lower 

 forms of animals are in the genetic line of (h?velo]nnent of the higher forms ; that man, for 

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

 requires all forms of life to bo developed from some antecedent form, presumably, and m most 



cases certainly, lower in the scale of or- 

 ganization. Thus man and the gorilla 

 are botli descendants of some common 

 progenitor, more or less unlike cither of 

 these existing creatures. All mammals 

 are similarly the modified descendants of 

 s(jme more primitive stock, from wljich 

 stock sprang also all Sauropsida, medi- 

 ately or immediately; therefm-e, a Mam- 

 mal is not a modified Bird, though higher 

 in the scale ; and, th(jugh a Bird is a 

 modified Reptile, it is not a modification 

 I if any such snake or lizard as now ex- 

 ists. The most bird -like reptiles known 

 are not the Pterodactyls, or Flying Rep- 

 tiles (Pterosauri({), as might be sup- 

 ]iosed; but of that remarkable order, the 

 OrniihosceUda, comprising the Dinosan- 

 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- 

 tratiiig also tlie art of lithography in the Jurassic period, 

 engraved by Arclimopteryx lithofjraphlca. From the original 

 slab in the British Museum ; after A. Newton, Encij. Brit. 



Geologic Succession of Birds. — 



Birds have been traced back in geologic 

 time to Cretaceous and Jurassic epochs 

 of the Mesozoic or Mid-Life period of 

 the world's history. Tlie earliest ornith- 



