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. 



