324 INTRODUCTION TO ZOOLOGY. 



of the dog, the 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 pleasure, 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 geographical distribution are more potent than the man- 

 date of the king who placed his chair upon the beach, and 

 forbade the approach of the waves ''Thus far slialt thou 

 come, and no further." 



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, from the equator to the 

 poles. 



The number of species is greatest towards the equator, 

 except among the aquatic tribes. Europe is regarded as 

 remarkably rich in the number of its birds, the species 

 amounting, according to a catalogue* published in 1840,f to 

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

 sixty-four genera. It is interesting to observe the compara- 

 tive numbers belonging to the leading groups: 



Rapacious Birds 54 species. 



Perching and Climbing Birds 209 , , 



Scraping Birds 28 , , 



Wading Birds 97 ,, 



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 6,266 

 species; but Mr. Strickland is of opinion that 5,000 species 



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

 from Berghaus's and Johnston's Physical Atlas : a highly valuable work, 

 which has been referred to on the distribution of reptiles. 



t By Keyserling and Blasius. 



