REACTIONS OF A. TIGRINUM 263 



but keep swimming on and do not stop at the point of the diffu- 

 sion which would supposedly be, in this case, the center of at- 

 traction. This stimulus is not sufficiently definite and the 

 animal swims about until attracted (by sight) to the motion of the 

 piece of worm, which is then seized. 



The same indications are given with beef juice or with strips 

 of beef instead of earthworm. The animals are stimulated by 

 the diffusion, but seldom engulf the food if it remains motionless. 

 When the strip of beef is moved by means of an attached thread, 

 the animal is quickly attracted and speedily engulfs it. 



The eyeless forms, under the same conditions, also show signs 

 of stimulation. Their ability to locate food is less than that of 

 the normal larvae. They are easily attracted to any slightly 

 mo\ing object, and since they lack the sense of sight it must 

 be concluded that there is another factor entermg into the reac- 

 tion, that of sensitivity to vibration stimuli. Under conditions 

 of starvation, an increase in sensitivity to the diffusion of passive 

 or motionless objects must result, for the eyeless larvae will 

 locate and devour the fecal material within the aquaria. 



The noseless forms are not stimulated by diffusing substances. 

 They swim passively about the aquaria after the introduction of 

 food materials of different sorts and unless the food exhibits 

 motion it is entirely overlooked. Pieces of beef are completely 

 ignored, producing no modification in the behavior of the animal 

 unless they are agitated, when they are quickly engulfed. 



These experiments, made on larvae of Amblystoma tigrinum, 

 thus confirm the results of Burr ('16), who used A. punctatum. 

 The work has been further extended by the study of individuals 

 deprived of both eyes and nose. 



The eyeless and noseless forms show the same behavior as 

 the noseless. In general, these larvae remain quiet in the aquaria 

 and move about only at intervals. They are absolutely de- 

 pendent upon mechanical stimuli in finding food. This is clearly 

 shown by the way in which they ignore organic material such as 

 killed earthworm or bits of beef. Under conditions of starva- 

 tion, they exhibit a certain foraging reaction, pushing the objects 

 about within the aquarium in order to discover whether inherent 



