146 ON THE INSTINCTS OF BIRDS. 
It appears, then, from the foregoing observations, 
that the principal actions of birds, though liable to 
be considerably modified by the operations of the 
intellectual powers and changes of organization, as 
well as by various external circumstances, are, con- 
trary to the opinion of Dr. Darwin, decidedly of in- 
stinctive origin. Many additional arguments might 
be advanced, and a multitude of highly respectable 
authorities quoted in support of this doctrine ; but, 
conceiving that sufficient evidence has been already 
produced, I shall only add that I am not aware of 
any serious objection which can be urged against it. 
