4 DISTRIBUTION OF BIRDS. 



in minor jDoints, is still near enough to the truth to give 

 a correct idea of this extraordinary bird's appearance. 



The Arclui^opteryx was about tlie size of a Crow. Its 

 long, feathered tail is supposed to have acted as an aero- 

 plane, assisting in the support of the bird while it was 

 in the air, Init its power of flight was doubtless limited. 

 It was arboreal and probably never descended to the 

 earth, but climbed about the branches of trees, using its 

 large, hooked fingers in passing from limb to limb. 



The wanderings of this almost quadrupedal creature 

 must necessarily have been limited, but its winged de- 

 scendants of to-day are more generally distributed than 

 are any other animals.* They roam the earth from pole 

 to pole ; they are equally at home on a wave-washed 

 coral reef or in an arid desert, amid arctic snows or in 

 the shades of a tropical forest. This is due not alone to 

 their powers of flight but to their adaptability to vary- 

 ing conditions of life. Although, as I have said, birds 

 are more closely related among themselves than are the 

 members of either of the other higher groups of animals, 

 and all birds agree in possessing the more important 

 distinguishing characters of their class, yet they show a 

 wide range of variation in structure. 



This, in most instances, is closely related to habits, 



* On the distribution of animals read Allen, The Geographical 

 Distribution of North American Mammals, Bulletin of the American 

 Museum of Natural History, New York city, iv, 1892, pp. 199-244; 

 four maps. Allen, The Geographical Origin and Distribution of North 

 American Birds considered in Relation to Faunal Areas of North 

 America, The Auk (New York city), x, 1893, pp. 97-150; two maps. 

 Merriam, The Geographic Distribution of Life in North America, with 

 Special Reference to Mammalia. Proceedings of the Biological Society 

 of Washington, vii, 1892, pp. 1-64; one map. Merriam, Laws of Tem- 

 perature Control of the Geographic Distribution of Terrestrial Ani- 

 mals and Plants, National Geographic Magazine (Washington), vi, 

 1894, pp. 229-238 ; three maps. 



