308 INTEODUCTION TO ZOOLOGY. 



mewing of the cat, the creaking of a passing wheelbarrow, 

 follow with great truth and rapidity." 



Distribution.— To one who regarded only the powers of 

 flight which birds possess, it might seem easy for beings so 

 endowed to change their abode at pleasm-e, and not, like the 

 more slow-moving mammalia, be restricted to certain regions ; 

 but here, as in every other department of Zoology, the laws of 

 geogi-aphical distribution are more potent than the mandate of 

 the king who placed his chair upon the beach, and forbade the 

 approach of the waves — " Thus far shalt thou come, and no 

 fui-ther." 



The number of species is supposed to be about four times 

 greater than that of quadrupeds ; and, with the exception of 

 fishes, they are more widely distributed than any other class 

 of vertebrated animals. Mammalia and reptiles are, to a 

 great extent, limited to the warmer regions ; but birds are 

 found in every part of the earth, froai the equator to the 

 poles. 



The number of species is greatest towards the equator, 

 except among the aquatic tribes. Europe is regarded as re- 

 markably rich in the number of its birds, the species amount- 

 ing, according to a catalogue* published in 1840,t to 490, 

 arranged in thirty -four families, and one hundred and sixty-four 

 genera. It is interesting to observe the comparative numbers 

 belonging to the leading groups : — 



Rapacious Birds 54 species. 



Perching and Climbing Birds . . . 209 „ 



Scraping Birds 28 „ 



Wading Birds 87 „ 



Swimming Birds 112 „ 



Total . . . 490 species. 



Classification. — The number of species at present known to 

 naturalists is in some degree doubtful, for the same bird has 

 frequently appeared under more than one name, in the works 

 of successive authors. Lesson has enumerated G,2GG species ; 

 but Mr, Strickland is of opinion that 5,000 species are pro- 



* This and all other information on the subject of distribution is derived 

 from Berghaiis's and Johnston's I'hysical AtLos: a highly valuable work, 

 ■fi'liicli has been referred to on tlie distribution of reptiles. 



t By Keyserling and Blasius, 



