WHAT DO ANIMALS KNOW? 
inherited knowledge, the amount left, representing 
its own power of thought, would be very small. Dar- 
win tells of a pike in an aquarium separated by 
plate-glass from fish which were its proper food, and 
that the pike, in trying to capture the fish, would 
often dash with such violence against the glass as to 
be completely stunned. This the pike did for three 
months before it learned caution. After the glass 
was removed, the pike would not attack those par- 
ticular fishes, but would devour others that were in- 
troduced. It did not yet understand the situation, 
but merely associated the punishment it had received 
with a particular kind of fish. 
During the mating season the males of some of 
our birds may often be seen dashing themselves 
against a window, and pecking and fluttering against 
the pane for hours at a time, day after day. They 
take their own images reflected in the glass to be 
rival birds, and are bent upon demolishing them. 
They never comprehend the mystery of the glass, be- 
cause glass is not found in nature, and neither they 
nor their ancestors have had any experience with it. 
Contrast these incidents with those which Dar- 
win relates of the American monkeys. When the 
monkeys had cut themselves once with any sharp 
tool, they would not touch it again, or else would 
handle it with the greatest caution. They evinced 
the simpler forms of reason, of which monkeys are 
no doubt capable. 
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