REACTIONS OF A. TIGRINUM 269 



short while, makes for the glass tube, approaching it from closed 

 end which was purposely placed toward center of aquarium while 

 open end of tube was situated toward side of aquarium and 

 touching it. After nosing tube, animal follows up side of tube 

 to get to open end, pushing tube across aquarium in an effort to 

 obtain diffusing contents. An empty vial produced no reac- 

 tion. 



Throughout this series of experiments, the reaction to the vial 

 filled with earthworms was much faster than that given to the 

 test sacks. The amount of diffusion is greater in the vial experi- 

 ments and the diffusion takes place from one side of a definite 

 focus in contrast to the test sacks which diffuse on all sides. It 

 is likely that the strength or concentration of the diffusing sub- 

 stances plays a large part in the difference of the speed of the two 

 reactions. 



Reactions to jnoving objects. The animals were subjected to 

 tests with moving objects as in the preceding section. One 

 tj^ical case will suffice to show the manipulation used and the 

 general result. 



Trial 1. Animal B. Sand bag twitched gently in front of 

 animal. Animal follows bag as it is drawn across the aquarium. 

 Animal noses bag when it comes to rest. No further reaction. 

 Trial repeated with same result. Earthworm bag twitched be- 

 fore animal. Response immediate, animal follows, noses when at 

 rest and seizes. 



The reaction time of normal animals in darkness is much slower 

 than the reaction time in the fight, but none the less definite. 

 The sensitivity of the animal to vibration stimuU seems to be 

 increased, as shown by the fact that the animal will follow the 

 sand bag although moved very gently so that the amount of 

 motion given to the surrounding medium is quite small. 



If.. Experiments upon nose-stopped animals 



Many methods for occluding the sense of smell have been 

 tried by experimenters. The closure of the external nares by 

 stitching has been used by Parker and his coworkers. The 

 cotton-wool plug used by Sheldon and later by Parker has been 



