CLASS AVES 



'(THE BIRDS.) 



Birds are warm-blooded, air-breathing vertebrates, with a covering of feathers; 

 a complete double circulation; the two front limbs (wings) adapted for flying or 

 swimming, the two back limbs (legs) adapted for walking or swimming; respira- 

 tion by lungs, which are connected with air cavities in various parts of the body. 

 Birds are born from eggs, which are fertilized within the body, and hatched exter- 

 nally, either by incubation or heat of the sun; the shell is limy, hard and brittle. 



More might be said, but the obvious mark is this : Birds are the only animals 

 which have feathers. 



The classification of birds is unsettled. Existing birds are so closely related 

 they might properly be placed in one order, called by Professor Gill Eurhipidura. 

 Professor Huxley unites all birds having (usually) the power of flight and a verti- 

 cal ridge or keel on the breast-bone in one order, the Cajinatcc ( birds with a keeled 

 sternum); the birds having a smooth or raft-like breast-bone, as the ostrich, rhea, 

 emu, cassowary, the small apteryx oi New Zealand, and those "giants of feather- 

 dom," the huge species of diornis, are placed by the same author in order RatitcE. 

 The extinct Archeopteryx, found fossil in the lithographic slates of Solenhofen, 

 Bavaria — a reptile-like bird, having teeth, claws on its wings, and a lizard-like tail 

 longer than the body, forms a third natural order, the Saunms (lizard-like birds). 



The term "order," as generally used in Ornithology, is applied to nearly a score 

 of variously related groups of birds and does not imply such fundamental differ- 

 ences of structure as those pointed out above, nor, indeed, such differences as exist 

 between the "orders" of reptiles and fishes. 



For convenience in identification, we insert here an artificial key to the 



ORDERS OF INDIANA BIRDS, 



*Toe5 3; two in front, one back, (Three-toed Woodpeckers). . Picarice, B. 



**Toes 3 ; all in front. (Snipe, plover.) . . . . , Limicola, F. 



***Toes 4; two in front, two behind. 



Bill cered and hooked. (Parrots.) .... Psitiaci, B. B. 

 Bill lengthened ; no cere or hook. (Woodpeckers.) . Picaria, B. 

 **** Toes 4; three in front, one behind. 

 I. Toes not webbed at all. 



a. Hind toe on a level with front toes. 



b. Nose holes under a soft, tumid membrane ; head small ; tarsus reticulate 

 behind. (Pigeons and doves.) ..... ColumbcE D. 



