CHARACTERS OF A BIRD. 393 



The characteristics of a bird are given in the 

 following very concise language by Professor 

 Owen. " It is an oviparous* animal, with warm 

 blood, a double circulation, and a covering of 

 feathers. The fore-limbs, or wings, are invariably 

 constructed according to that plan which best 

 adapts them for the actions of flight ; and although 

 in a few instances the development of the wings 

 proceeds not so far as to enable them to act upon 

 the surrounding atmosphere with sufficient power 

 to overcome the counteracting force of gravity, 

 yet in these cases they assist by analogous motions 

 the posterior extremities the legs, either as in the 

 ostrich, by beating the air while the body is carried 

 rapidly forward by the action of the powerful legs, 

 or, as in the penguin, by striking the water after 

 the manner of fins, and by the resistance of the 

 denser medium carrying the body through the 

 water in a manner analogous to that by which the 

 birds of flight are borne through the air. In a few 

 exceptions only are the wings reduced to mere 

 weapons of offence, as in the cassiowary, and in 

 the singular apteryx of New Zealand, in which 

 they are represented by a single spur. In no 

 instance do the wings take any share in stationary 

 * Producing the young inclosed in a shell. 



