The Problevi of Adaptation 5 



turbed, the birds at once squat down on the ground, and 

 remain perfectly quiet until the danger is past. Their re- 

 semblance to the ground is so perfect that they are almost 

 invisible so long as they remain quiet. If, instead of remain- 

 ing still, they were to attempt to run away when disturbed, 

 they would be much more easily seen. 



Certain solitary wasps {Ammophila) have the habit of 

 stinging caterpillars and spiders, and dragging them to their 

 nests, where they are stored away for the future use of the 

 young that hatch from the eggs laid by the wasp on the 

 body of the prey. As a result of the sting which the wasp 

 administers to the caterpillar, the latter is paralyzed, and 

 cannot escape from the hole in which it is stored, where it 

 serves as food for the young wasp that emerges from the 

 egg. It was originally claimed by Forel that the wasp stings 

 the caterpillar in such a way that the central nervous system 

 is always pierced, and many subsequent naturalists have mar- 

 velled at the perfection of such a wonderful instinct. But 

 the recent results of the Peckhams have made it clear that 

 the act of the wasp is not carried out with the precision 

 previously supposed, although it is true that the wasp pierces 

 the caterpillar on the lower surface where the ventral chain 

 of ganglia lies. The habit of this wasp is not very dissimilar 

 from that shown by many other kinds of wasps that sting 

 their captive in order to quiet it. We need not imagine in 

 this case that the act carries with it the consciousness that 

 the caterpillar, quieted in this way, will be unable to escape 

 before the young wasps have hatched. 



The resemblance in color of many animals to their natural 

 backgrounds has in recent years excited the interest and 

 imagination of many naturalists. The name of protective 

 coloration has been given to this group of phenomena. The 

 following cases which have less the appearance of purely 

 imaginative writing may serve by way of illustration. A 

 striking example is that of the ptarmigan which has a pure 



