60 SECRETS OF ANIMAL LIFE 



to the floor of the aquarium. One arm was made 

 rough internally, and at its upper end the snail 

 received an electric shock, of which the roughness 

 was meant to be the " warning." The smooth arm 

 of the tube led to the surface of the water, where 

 fresh air is obtained sufficient reward in itself. 

 The experiment consisted in pressing the air from 

 the snail's lung and then placing it at the base of 

 the so-called labyrinth. It is of value to the snail 

 to get its lung filled as soon as possible; this is 

 attained by creeping up the smooth arm, it is missed 

 by creeping up the rough one; and the failure is 

 emphasized by a mild punishment, the slight electric 

 shock. But the result of the pretty experiment was 

 to show a complete incapacity to profit by experi- 

 ence to the extent of solving the problem. The 

 percentage of error did not diminish as the series 

 of trials lengthened; indeed, things sometimes got 

 worse instead of better. 



In one interesting set of experiments a power of 

 forming associations was displayed, but it was 

 not, so to speak, followed up. Both arms were 

 smooth, but the wrong road had as its warning 

 notice-board an irritating hair which was made to 

 touch the snail's horns and the back of its head. 

 Immediately on the heels of the warning, if the 

 snail persisted on its wrong course, came the punish- 

 ment of a shock. Now, in 15.6 per cent out of a 

 total of nine hundred and thirty trials, the snails 

 changed their course from the wrong to the right 

 path after contact with the warning stimulus, but 



