144 THE MEANING OF EVOLUTION 
of scarcity of cicadas, but the killer has apparently 
little difficulty in finding his prey. The wasp pounces 
upon the insect, and in spite of its strength and the 
thrashing of its vigorous wings punctures it with his 
sting again and again. The poison of the sting enter- 
ing into the nerve centers gradually paralyzes, but 
usually does not kill, the cicada. Now the killer car- 
ries its prey home, pushes it to the bottom of the tun- 
nel and deposits upon it a single egg. The wasp 
closes up the hole and leaves the place. When the egg 
hatches and the grub of the wasp emerges, it finds a 
big cicada just at hand, upon which it feeds. By the 
time the cicada is completely devoured, the wasp grub 
has obtained its full growth. After a short period of 
development a new sphex wasp is ready to work its 
way out of the tunnel, find a mate, dig a hole, and 
safely provide for its own children. 
Still more remarkable adaptations for the care of 
the young appear among the birds. Here the eggs are 
not to be deserted, but are to be cared for until the 
young appear. These again must have attention until 
such time as they are quite able to take care of them- 
selves. The birds are warm-blooded animals, and 
even their young, while they are developing in the 
egg, are warm-blooded. Consequently the tempera- 
ture of the egg must be maintained evenly and uni- 
formly, or there will be no development. 
