OR, PLAIN 



short distances. On the con- 

 trary, the tail of the swallow, 1, 

 is of great length, by which the 

 bird is enabled instantly to change 

 the direction of its flight. In 



5 



388. 



some instances, where the tail is 

 less developed, the primaries of 

 the wings extend beyond the 

 tail, and in flight are thrown 

 back, and made to do its office, 

 as in the case of the long winged 

 swift, 5. In other cases, the legs 

 and feet being long, are thrown 

 lack, 6, as in the instance of the 



7 



389. * 



stork, 7, and made to act as a 

 substitute for the tail. The 

 principal forms of birds' tails, are 

 square, or even tipped, as in 



TEACHING. 107 



388 ; rounded, as in 430 ; gra- 

 duated symmetrically on each 

 side, as in 425 ; irregularly , 

 some feathers growing to greater 

 length than others, as in the 

 hjre bird- slightly forked, with 

 rounded points, as in the kite; 

 forked, with sharp points, as in 

 386 ; plumose, as in the fowl, 

 G-381. 



The eyes of birds, 8, are gene- 

 rally large ; their vision acute ; 

 by peculiar anatomical structure, 

 birds of prey can adjust their 

 eyes to very long or short dis- 

 tances, upon the principle of the 

 telescope. The faculty of sight 

 being of great importance, on 

 account of the swiftness of their 

 flight, and the necessity of de- 

 scrying their food among particles 



8 . 



390. 



of earth, and upon the trunks, 

 branches, and leaves of trees, 

 they are provided with extraor- 

 dinary means for the preserva- 

 tion of their eyes. They have 

 three eyelids : an upper and 

 lower, and a semi-transparent 

 membrane, which is folded in one 

 corner of each eye, and drawn 

 across it like a curtain, when 

 occasion requires, by muscular 

 threads. This thin membrane is 

 used when birds are flying high 



