36 BIRDS. 



55. 



(The Birds.) 



A Bird may be defined as an air - breathing vertebrate 

 with a covering of feathers; warm blood; a complete 

 double circulation; the two anterior limbs (wings) 

 adapted for flying or swimming, the two posterior limbs 

 (legs) adapted for walking or swimming; respiration 

 never effected by gills or branchiae, but, after leaving 

 the egg, by lungs which are connected with air cavities 

 in various parts of the body. Reproduction by eggs, 

 which are fertilized within the body and hatched 

 externally, either by incubation or exposure to the heat 

 of the sun; the shell calcareous, hard and brittle. 



. Much more might be added, but the obvious distinction 

 is this: All Birds have feathers, and no other animal 

 has feathers. 



The classification of this group, as of most others, is 

 still in an unsettled condition. Strictly speaking, the 

 existing members of the class are so closely related that 

 they might, with propriety, be combined into one order, 

 which, by Prof. Gill, has been named EUEHIPIDUEA. At 

 present, however, the term " order " may be applied to 

 the groups so designated below, without thereby implying 

 any such structural differences as exist between the 

 " orders " of Reptiles or Fishes. 



We now proceed to an artificial key to the 



ORDERS OF BIRDS. 



* Toes 3 : two in front, one behind. . . . PTCARLE, H. 

 ** Toes 3: all in front; toes cleft or semipalmate. LIMICOL^J, M. 



