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INTELLIGENCE IN LOWER VERTEBRATES 219 
for a career of an almost unlimited mental development. 
The molluscs and the arthropods, on the other hand, have a 
different sort of a brain. They havenocerebral cortex; there- 
fore they cannot form associations and consequently they are 
but more or less complicated “reflex machines.” So with 
certain of the vertebrates, the bony fish whose cerebral 
cortex is represented by a membrane of non-nervous tissue 
over the basal ganglionic centers, they too must be chained 
down to the routine life of reflexes and instincts, with no 
power of learning, no ability to profit by experience. So 
our comparative anatomist might have argued and so indeed 
some comparative anatomists have argued. This contention 
as we have seen is far from justified in the arthropods, and 
we shall see that it is equally groundless as regards the 
vertebrates with no cerebral cortex. 
Every angler can doubtless furnish evidence of the learning 
of fishes. In trout streams that have been much frequented 
the fish become much more wary of the bait than at first, 
and some of the old, experienced fishes can be induced only 
with great difficulty to take the line. On the other hand, 
certain fish will allow themselves to be caught and hauled 
out of the water repeatedly without conquering their pro- 
pensity to dart at the bait. 
No one can read very much in comparative psychology 
without frequently encountering the story of Mébius’ pike 
—a story which the professor was fond of repeating in 
his lectures and which came to be looked forward to as a 
regular annual event by his students. This celebrated pike 
was kept in a part of an aquarium separated by a glass plate 
from an adjoining part which contained several minnows. 
The pike made frequent dashes for the minnows and each 
time received a bump against the glass plate. After about 
three months of attempts to catch the minnows the pike 
ae 
