xin PHYLUM CHORDATA 415 



in the Palrearctic and most of the Neartic region, the Finches in 

 the Australasian region, as well as in New Zealand and Polynesia, 

 and the Starlings in both regions of the New World. 



Birds are comparatively rare in the fossil state : their powers of 

 flight render them less liable to be swept away and drowned by 

 floods and so imbedded in deposits at the mouths of rivers or in 

 lakes. Up to the cretaceous period, Archseopteryx, from the 

 Lower Jurassic, is the only Bird known. In the Cretaceous of 



* t, 



North America toothed Birds of the orders Odontolcae and 

 Ichthyorm'thes make their appearance, while in the Eocene 

 numerous interesting forms occur, including the Gastornithes and 

 the Stereornithes. 



Ethology. It is impossible here to do more than allude, in the 

 briefest way, to the immense and fascinating group of facts relating 

 to the instincts, habits, and adaptations found in the present class. 

 Their social instincts, their song, their courtship customs, the 

 wonderful advance in the parental instinct, leading to diminished 

 mortality in the young, are all subjects for which the reader 

 must be referred to the works on general Natural History men- 

 tioned in the Appendix. The same applies to the puzzling 

 subject of migration, which will be referred to in the Section on 

 Distribution. 



Phylogeny.- -That Birds are descended from Reptilian ances- 

 tors, that they are, as it has been said, u glorified Reptiles," seems 

 as certain as anything of the kind can well be. Apart from the 

 direct evidence afforded by Archseopteryx and by the numerous 

 avian characteristics of Dinosauria and Ornithosauria, the indirect 

 evidence of anatomy and embryology is very strong. The single 

 occipital condyle, the six bones to each mandibular ramus, the ankle- 

 joint between the proximal and distal tarsals, the number of 

 phalanges in the digits of the foot, the epidermal exoskeleton, 

 partly taking the form of scales, the meroblastic egg with large 

 food yolk, the amnion, and the respiratory allantois, are all 

 characters common to Birds and Reptiles and not found together, 

 indeed for the most part not found at all, in any other class. For 

 this reason Reptiles and Birds are often conveniently grouped 

 together, as already stated (p. 291), as Sauropsida. 



It seems probable that the earliest Birds could fly, and that their 

 evolution from Reptilian ancestors was directly connected with the 

 assumption of aerial habits. It is not unlikely that these ances- 

 tors possessed a patagium, like that of Ornithosauria, and that, as 

 the scales of the fore-limb developed into feathers, this organ was 

 gradually reduced to the small pre- and post-patagia of the exist- 

 ing Bird's wing. What was the nature of the Reptilian ancestor 

 is a question as yet quite unsolved. It can hardly have been a 

 Pterodactyle, since in that order the modification of the fore-limb 

 has proceeded on entirely different lines from those which charac- 



