THE KDUCABILITY OF THLIKE liOCKLhSGis. 2\i6 



was not until J)ecembei' '27th (nineteenth day) that it could 

 definitely be noted that the Bullhead had begun to associate the 

 illumination of the aquarium, and subsequent introduction of 

 the forceps into the Avater, with the advent of food. On 

 December 28th, when the surface of the water was disturbed 

 with the forceps, the Bullhead looked up with the characteristic- 

 ally scrutinising glance of this species of fish, and then excitedly 

 snapped at fragments of seaweed which were caused to move by 

 the agitated water. On the 31st (twenty-third day) the Bullhead 

 approached, with unmistakable eagerness for food, the glass front 

 of the aquarium, when the electric light was turned on and the 

 glass tapped with the fingers ; and then it swam in its usual 

 heavy fashion to the surface of the water as though anticipating 

 the introduction of food there. On January 5th (twenty-eighth 

 day), when the light was turned on, the Bullhead darted to the 

 surface and put its snout out of the water several times. It 

 then retreated to the top of the rockwork, which is four inches 

 from the surface. A finger was put into the water, with its 

 tip just beneath the surface, and the Bullhead made several darts 

 towards it. The fish then received pieces of mussel from my 

 fingers. By this time the Bullhead had apparently lost all fear 

 of human beings, and it seemed to be in no way alarmed — 

 indeed, it scarcely noticed— a gentle thrust from a finger or 

 from the forceps. On the morning of January 11th the fish 

 would not trouble itself to move from a certain place until it 

 had received several thrusts of increasing force from the forceps. 

 On the 15th (thirty-eighth day) it darted to the glass, against 

 which a piece of mussel was held ; it then followed the food as 

 it was slowly dragged up the glass to the surface ; there the 

 mussel was taken by the fish from my fingers. From about that 

 date onwards, a few taps upon the glass, preceded or not by 

 illumination of the tank, was sufficient to bring the Bullhead, if it 

 had not been fed, eagerly to the front of the aquarium. The 

 fish died in July, but before this time it had become so confident 

 that it was sometimes possible to take it in the fingers for 

 examination, but not, of course, to lift it out of the water. 



