The Problem of Adaptation 3 
of the outer surface of the tibia is arched over by stiff 
hairs. The poller: collected from the stamens of flowers 
is stowed away in this receptacle by means of the other 
pairs of legs. “The structure is unique, and is not found in 
any other insects except the bees. It is, moreover, present 
only in the worker bees, and is absent in the queen and the 
males. 
The preceding cases, in which the adapted parts are used 
for the ordinary purposes of life of the individual, are not 
essentially different from the cases in which the organ is 
used to protect the animal from its enemies. The bad taste 
of certain insects is supposed to protect them from being 
eaten by birds. Cases like this of passive: protection grade 
off in turn into those in which, by some reflex or voluntary 
act, the animal protects itself. The bad-smelling horns of 
the caterpillar of the black swallow-tailed butterfly (Papzlio 
polyxenes) are thrust out when the animal is touched, and it 
is believed that they serve to protect the caterpillar from 
attack. The foetid secretion of the glands of the skunk is 
believed to serve as a protection to the animal, although the 
presence of the nauseous odor may lead finally to the exter- 
mination of the skunk by man. The sting of bees and of 
wasps serves to protect the individual from attack. The sting 
was originally an ovipositor, and used in laying the eggs. 
It has, secondarily, been changed into an organ of offence. 
The special instincts and reflex acts furnish a striking 
group of adaptations. The building of the spider’s web is 
one of the most remarkable cases of this kind. The con- 
struction of the web cannot be the result of imitation, since, 
in many instances, the young are born in the spring of the 
year following the death of the parents. Each species of 
spider has its own type of web, and each web has as char- 
acteristic a form as has the spider itself. It is also important 
to find that a certain type of web may be characteristic of 
an entire family of spiders. Since, in many cases, the web 
