CLASSIFICATION OF BIRDS. 



43 



silently and iniperceptibh' relaxes into the mildness of spring — can he fix, I say, upon 

 the exact period \yheu the former teiminates, and the latter begins ? Can he assert, at 



FIG. 28, 



one moment, that he is within the precincts of one season, and that, even while he 

 speaks, he has passed into the confines of the other. He may, it is true, assign artificial 



