560 STRUCTURAL CHARACTERS 



mark a new era in ornithology ; for they have brought together all the known facts and have 

 pointed the way for further lines of profitable research. 



All systems of classification, based on descent, must have apparent breaks ; for we are dealing 

 with different branches of a common stem, and one branch, with its ramifications, must be taken 

 at a time. A linear arrangement from "highest" to "lowest," or vice versa, is impossible. 

 The Passerine and Coraciiform birds must, for example, be taken together. They are divergent 

 branches of a common stem, only very remotely related to any other branches of existing birds. 



Having disposed of these, one turns next to that great assemblage which includes the 

 Pigeons and Sandgrouse, Gulls, Auks and Plovers ; Bustards, Cranes and Rails ; and the Game- 

 birds these are ramifications of another great branch of the phylogenetic tree. Next come 

 the Accipitres, Storks, Steganopodes and Anseres, and finally the Petrels and Divers. The like- 

 nesses which form such pitfalls, between birds like Swifts and Swallows, Owls and Accipitres, 

 Cranes and Storks, for example, are accidental, or rather are due to convergence through adapta- 

 tion to like needs. As well might one classify Whales and Ichthyosaurs, Newts and Crocodiles, 

 because these present certain features in common. The smooth running of one type into 

 another, which the systematic ornithologist so commonly strives to achieve, can lead only to 

 confusion. He is attempting the impossible, and making confusion worse confounded. 



The following " key " is intended for those who are taking up the study of ornithology 

 and are therefore unfamiliar with any save the commonest species of our native birds. 

 Having a specimen which puzzles him, it is assumed that he will turn to this key and 

 endeavour to " run down " his bird : discovering first the order to which it belongs, then 

 passing to the family, thence to the genus. Having found this, the rest is comparatively 

 easy. But even then his difficulties may not be over, for it is by no means easy in some cases 

 to make some specimens agree with written descriptions, owing to the fact that they may 

 present intermediate stages between say the juvenile and adult dress, or the nuptial and 

 winter plumages, which seem difficult to reconcile with any given description. But then it 

 will generally be found that identification is possible by the process of elimination. 



GLOSSARY OF TERMS USED IN THE KEY TO THE 



CLASSIFICATION ADOPTED 



I. EXTERNAL CHARACTERS. 



Acrotarsium* the front part of the tarso-metatarsus. 



Apteria the areas of the body not covered by contour feathers. 



Cavernum the enlarged cavern-like chamber which forms the external aperture of the ear in 



the Owls. 



Culmen* the ridge of the beak. 



Diastataxic wings wherein the fifth pair of major secondary coverts do not embrace a remei. 

 Eutaxic wings in which each pair of major secondary coverts embraces a remex. 

 Fossa a cavity or depression. 

 Hallux* the hind-toe. 



Manus the hand, that portion of the wing skeleton which supports the primaries.* 

 Nares the nostrils. 

 Operculum applied to the fleshy flap covering the nostrils, e.g. Pheasant, and to the large, 



semicircular fold of skin covering the external aperture of the ear of the owls of the 



genus Asia. 



PamprodactylouA all the toes turned forwards. 

 Planta* the sole or hinder border of the tarso-metatarsus. 



* Illustrated on p. xiv, vol. i. See List on p. xv. 



