The Problem 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. Asa 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 
