THE NERVOUS SYSTEM. 183 
they select with wonderful sagacity; and Monkeys avoid 
poisonous berries; Bees and Squirrels store up food for 
the future; Bees, Wasps, and Spiders construct with mar- 
velous precision ; and the subterranean chambers of Ants 
and the dikes of the Beaver show engineering skill; while 
Salmon go from the ocean up the rivers to spawn; and 
Birds of the temperate zones migrate with great regular- 
ity. 
But in the midst of this automatism there are the glim- 
merings of intelligence and free-will. We see some eyi- 
dence of choice and of designed adaptation. Pure instinct 
should be infallible. Yet we notice mistakes that remind 
us of mental aberrations. Bees are not so economical as 
has been generally supposed. A mathematician can make 
five cells with less wax than the Bee uses for four; while 
the Humble-bee uses three times as much material as the 
Hive-bee. An exact hexagonal cell does not exist in nat- 
ure. Flies lay eggs on the carrion-plant because it hap- 
pens to have the odor of putrid meat. The domesticated 
Beaver will build a dam across its apartment. Birds fre- 
quently make mistakes in the construction and location of 
their nests. In fact, the process of cheating animals relies 
on the imperfection of instinct. Nor are the actions of 
the brute creation always perfectly uniform; and so far 
as animals conform to circumstances, they act from intel- 
ligence, not instinct. There is proof that some animals 
profit by experience. Birds do learn to make their nests; 
and the older ones build the best. Trappers know well 
that young animals are more easily caught than old ones. 
Birds brought up from the egg, in cages, do not make the 
characteristic nests of their species; nor do they have the 
same song peculiar to their species, if they have not heard 
it. Chimney-swallows certainly built their nests different- 
ly in America three hundred years ago. A Bee can make 
cells of another shape, for it sometimes does; its actions, 
