430 ZOOLOGY SECT. 



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, Archaeopteryx, from the 

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

 America toothed Birds of the orders Odontolcse and Ichthyornithes 

 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 mentioned 

 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 ancestors, 

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

 as certain as anything of the bind 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. 303), 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 ancestors 

 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 existing 

 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- 

 terise Birds ; it cannot well have been a Dinosaur, since we have 



