TEE BIRDS. 



211 



em States and passes northward, till in June it reaches 

 Canada and extends west to the Saskatchewan Eiver, in 54° 

 north latitude. 



SaysBaird : "While birds proceed generally in the spring 

 to the Tery spot of birth, and by a definite route, their re- 

 turn in autumn is not necessarily in the same line. Many 

 birds are familiar yisitors in abundance in certain locali- 

 ties in either spring or autumn, and are not known there 

 in the other season." He thinks that in very many in- 

 stances birds proceed northward along the valley of the 



Fib. 218.— Restoration of Archceopteryx macrm-a. After Owen. 



Mississippi, to return along the coast of the Atlantic. In 

 general, also, the northward vernal movement is performed 

 much more rapidly, and with fewer stops by the way, than 

 the autumnal. " Birds generally make their appearance in 

 given localities with wonderful regularity in the spring — 

 the SylvicolidcB especially; a difference of a few days in suc- 

 cessive years attracting the notice of the careful observer: 

 this difference is generally influenced by the season. The 

 time of autumnal return is, perhaps, less definite." 



The class of birds, so far as regards the living species, 

 is very distinct from any ether group of vertebrates, but 

 there is an extinct form, the Arehceopteryx (Fig. 318), 



