924 THE AMERICAN NATURALIST. [VoL XXXIII. 
slide (without any opening) in behind him at D and moving it 
gently from D to A and then place, say slide /, across the 
aquarium at 1, we shall have a chance to observe the animal’s 
behavior to good purpose. 
This fish dislikes the sunlight and tries to get back to D. 
He reacts to the situation in which he finds himself by swim- 
ming against the screen, bumping against it here and there 
along the bottom. He may stop and remain still for a while. 
He will occasionally rise up toward the top of the water, 
especially while swimming up and down the length of the 
i screen. When he happens 
to rise up to the top at the 
right-hand end, he has a 
Ad Boo A | clear path in front of him 
4 LAJ ae .:. 
D 
and swims to D and feels 
more comfortable. 
If, after he has enjoyed 
the shade fifteen minutes or 
more, you again confine him in A, and 
wf at Sa keep on doing so six or eight times a 
day for a day or so, you will find that 
he swims against the screen less and 
af e less, swims up and down along it fewer 
and fewer times, stays still less and 
less, until finally his only act is to go 
UL to the right-hand side, rise up, and 
swim out. In correspondence with 
this change in behavior you will find 
a very marked decrease in the time he takes to escape. The 
fish has clearly profited by his experience and modified his 
conduct to suit a situation for which his innate nervous 
equipment did not definitely provide. He has, in common 
language, /earned to get out. 
This particular experiment was repeated with a number of 
individuals. Another experiment was made, using three slides, 
ZI, IIT, and another, requiring the fish to find his way from A 
to B, B to C, and from C to D. The results of these and still 
others show exactly the same general mental process as does 
Fic. 2. 
