642 JONATHAN RISSER 



A number of trials in which the food was placed in the vessel 

 with the tadpoles showed that the reactions of the tadpoles 

 depended somewhat on the size of the vessel. In a small vessel 

 the time necessary for the food to be found by a certain number 

 of the tadpoles was usually less than in a larger vessel. The same 

 is true if the food is placed near the side of the vessel, say within 

 an inch of the side wall; in such a case the animal swimming 

 through the zone impregnated by the odor is influenced more 

 quickly than when the food is centrally placed. 



In the trials with two packets discrimination was very evi- 

 dent in the actions of the tadpoles. In the beginning of the 

 trial the reactions were at all times apparently without choice. 

 After the packets had been allowed to remain in the water for a 

 short time, the tadpoles always endeavored to feed from the 

 packet containing the food. Even if the tadpoles rested on the 

 'dummy' packet very little attempt was made to nibble. Trans- 

 position of the two packets was accompanied by a corresponding 

 redistribution of the tadpoles. 



This last method was modified several times, by exchanging 

 the envelopes of the packets, or by substituting an envelope 

 saturated with the odor of the food material for the food itself. 

 When this was done, the tadpoles congregated upon the food- 

 saturated envelope, finding it as they did the food open in the 

 water, or when contained in the envelope and allowed to remain 

 for some time. 



An attempt was made to determine whether the tadpoles 

 would orient themselves to an odor-saturated waterstream 

 which was allowed to flow into a vessel containing them; but 

 this experiment was fruitless of results, although there was some 

 slight evidence that the current was especially stimulating. 



Corroborative of the earlier findings of the experiments on the 

 two previous sets, experiments carried out with the third set 

 were of greater value in this study in what may be called operative 

 tests. 



To determine whether the reactions of the toad tadpoles 

 as already described are due solely to the stimulus received 



