EXTERNAL PARTS OF BIRDS.— FEATHERS. 81 



reference to the extraordinary form from the Jurassic and to the radical difference between 

 Ratite and Carinate Birds. The subclass Carinatce, which includes all other existing birds, seems 

 not to be primarily divisible into a few orders, such as were in vogue not many years ago; but to 

 be split directly into a large number — perhaps about twenty — groups of approximately 

 equivalent value, to be conventionally designated as orders, if we take CarinatcB as a subclass 

 of the class Aves. Passeres seems to be one of tiie most firmly established of these " ordinal " 

 groups ; but neither Passeres nor any other leading group of birds has any such taxonomic 

 grade as the groups of the same name have in other branches of zoology. ^^Picarice^^ is one 

 of the most unsatisfactory, and I have no doubt it will be abolished. The arrangement offered 

 on a subsequent page has perhaps some claims to consideration. 



With this glance at some taxonomic principles and practices, I pass to an outline of the 

 structure of birds, some knowledge of which is indispensable to any appreciation of orni- 

 thological definitions and descriptions. It is necessary to be brief, and I shall confine myself 

 mainly to consideration of those points, and explanation of those technical terms, which the 

 student needs to understand in order to use the present volume easily and successfully. Here 

 I will insert a tabular illustration of a sequence of zoological groups, from highest to lowest, 

 under which a bird may fall : — 



Kingdom, Animalia : Animals. 



Branch, Vertebrata: Back-boned Animals. 



Province, Sauropsida : Lizard-like Vertebrates. 

 Class, Aves: Birds. 



Subclass, Carinatce: Birds with keeled breast-bone. 

 Order, Passeres : Perching Birds. 



Suborder, Oscines : Singing Birds. 



Family, Turdidce: Thrush-like Birds. 



Subfamily, Turdince : True Thrushes. 

 Genus, Turdus : Typical Thrushes. 



Subgenus, Hylocichla : Wood Thrushes. 



Species, ustulatus : Olive-backed Thrush. 

 Subspecies, alicice : Alice's Thrush. 



§3. — DEFINITIONS AND DESCRIPTIONS OF THE EXTERIOR PARTS OF BIRDS. 



a. Of the Feathers, or Plumage. i 



Feathers are possessed only by birds, and all birds possess them. Feathers are therefore 

 diagnostic of the class Aves. Feathers are modified scales ; like scales, hair, horns, claws, etc., 

 tiiey are outgrowths of the integument, or skin covering the body, and therefore belong to tiie 

 class oi epidermic (Gr. eVi, epi, upon ; bipfia, derma, skin), or exoskeletal (Gr. e|, ex, out ; aKe'Kerov, 

 skeleton, dried; in the sense of " outer skeleton") structures. The horny coverings of beak 

 and feet are of the same class, but very difterently developed. The development of feathers is 

 a complicated process, and the result is correspondingly complex. Besides being the most 

 highly developed or specialized, wonderfully beautiful and perfect kind of tegumentary out- 

 growth — besides fulfilling in a singular manner the function of covering and protecting the 

 body — feathers have their particular locomotory office : that of accomplishing the act of flying 

 in a manner peculiar to birds. For all vertebrates, excepting birds, that progress through the 

 air — the flying ^»\\ {Exoccetus) with, its enlarged pectoral fins; the flying reptile (Draco or 

 Pterodacti/lus) with its skinny parachute ; the flying mammal (bat) witli its great webbed 

 fingers — accomplish aerial locomotion by means of tegumentary exjmnsions. Birds alone fly 



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