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 have no cerebral 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 Mobius' 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 



