122 THE MEANING OF EVOLUTION 
the very end of its life that the grasshopper has wings, 
and then they serve probably to aid in the search for 
a mate. Among the birds flight began simply in sail- 
ing out of the trees, into which the creature, still half 
lizard, had crept to escape its enemy. The earliest 
bird known to us had comparatively insignificant 
wings. There was really more support in its tail than 
in its wings, and this would distinctly indicate that it 
glided more than it flew. It had claws also upon its 
wings, and it was probably the case that this creature 
crept into the trees, at least in its earliest forms, and 
sailed down in a manner not unlike that employed 
to-day by the flying squirrel. From such simple be- 
ginnings came the wonderful power of flight in the 
birds. 
Among mammals the attempt to escape from the 
enemy has led to an interesting development, which 
will be more fully explained in a later section when we 
speak of the history of the horse. The early mam- 
mals walked flat-footed, as we do on our feet and as 
the raccoon and the bear do on theirs. Gradually, 
however, as their enemies became more fierce and bet- 
ter able to injure the larger mammals, the latter 
gained in power of flight, and this gain consisted first 
in rising from the toes, lifting the heels completely 
off the ground. At the same time the leg and foot 
were gradually lengthened. Doubtless in this way the 
