I INTRODUCTORY 3 
The bodies and brains of birds are suited to their 
full and varied life. Their circulation is rapid, their 
temperature higher than that of mammals, their lungs, 
though small, are probably the most efficient in the 
animal kingdom, their bones and their muscles have 
been adapted for purposes of flight, running, or swim- 
ming, they have brains that are, comparatively 
speaking, highly developed. 
And yet the bird is a near relation of the lizard. 
He is descended, unless nearly all our great authori- 
ties are at fault, though not from any existing reptile, 
yet from ancestors that were definitely reptilian. 
And yet how enormous is the difference between 
these descendants from the same stock! For the two 
lines must meet if we trace them upward far enough. 
A lizard is limited to earth, and even there his gait 
is an undignified shuffle. True, he slips with un- 
surpassed nimbleness into his hiding-place on a hot 
day when the sun has warmed his sluggish blood. 
But though he be the fastest of lizards, many a bird of 
no great size is a better runner, and could, without 
having recourse to the magic of wings, easily distance 
him in a race of more than a few yards. His forehead 
is low, hardly rising above his nose, showing, if 
other evidence were wanting, that his intellect is feeble. 
Indeed, in this respect, he is hardly above the boa- 
constrictor who mistakes his blanket for a rabbit 
and swallows it. His blood is cold, and when the 
thermometer sinks a little below the freezing-point 
he torpifies. In the winter he merely exists, while the 
bird lives. He eats but little and digests slowly— 
a sign of the sluggishness of his whole life. Both 
B 2 
