CHAPTER VIII 

 CLASS V. AVES (BIRDS) 



The propriety of giving class value to the birds is open to serious 

 question. Fundamentally birds are flying reptiles, highly specialized 

 for aerial locomotion. The close affinities of birds to reptiles was in 

 the mind of Huxley when he combined the two divisions under the 

 name Sauropsida. 



There is never the slightest difficulty in distinguishing a bird from 

 any other animal. The presence oi feathers is of itself a differentiating 

 character. All birds, moreover, are bipeds and have the fore limbs 

 modified as wings, which in some cases are rudimentary, in others, 

 secondarily specialized as flippers for swimming under water. The 

 absence of teeth and their replacement by the horny bill is a nearly 

 universal avian character. The tail is greatly reduced or foreshortened, 

 much as it is in man. There are not, except in certain domestic races 

 of fowls, more than four toes, of which one is the hallux or great toe. 

 Now none of these characters, except the possession of feathers, really 

 demarks the birds from the reptiles; for some group of reptiles, living 

 or extinct, is characterized by bipedahty, by wings, by beak, by lack 

 of teeth, by reduced tail, or by four toes. Is a bird then merely a 

 reptile with feathers? In a sense, yes; if feathers be taken as an index 

 of a complex of structural and functional adaptations for flight. The 

 bird, therefore, may be thought of as essentially a heavier-than-air 

 flying machine, a monoplane with propeller planes, a type of motor 

 mechanism that man has failed to duplicate. One of the most effect- 

 ive ways of presenting an account of the bird's characteristic struc- 

 tural and functional peculiarities is to compare it in considerable 

 detail with an aeroplane. 



The Bird an Automatic Aeroplane 



The essential features of a heavier-than-air flying machine are: — 

 1, Planes or wings; 2, great and sustained power, including fuel, 

 engine, propeller; 3, minimum weight consistent with maximum 

 rigidity of framework; 4, steering and balancing devices, including 



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