These experiments to test the effect of changing colors are also of interest in that they show in a remarkable way the influence of the direction of turning.  The animal after succeeding in getting around the first part of the labyrinth failed entirely to escape at the exit.  Here it should have turned to the left, instead of the right as it was accustomed to, but it persisted in turning to the right.  Fig. 3 represents approximately the path taken in the first trial; it shows the way in which the animal persisted in trying to get out on the right.  From this it is clear that both vision and the complex sensations of turning are important.

[Illustration:  FIG. 3.  Labyrinth with Conditions the Reverse of the Usual. (Compare with FIG. 2.) The colors as well as the partitions have been shifted.  The path is, approximately, that taken by No. 2 in the first trial after the reversal of conditions.]

The latter part of Table IV. presents further evidence in favor of vision.  For these tests the colors alone were reversed.  Previous to the change the animal had been making no mistakes whatever, thereafter there were four mistakes at the entrance and none at the exit.  Later, another experiment under the same conditions was made with the same animal, No. 2, with still more pronounced results.  In this case the animal went to the white, that is, in this instance, into the blind alley, and failed to get out; several times it jumped over to the left side (the open-passage side) of the box but each time it seemed to be attracted back to the white or repelled by the red, more probably the latter, as the animal had been trained for weeks to avoid the red.  Concerning the delicacy of visual discrimination I hope to have something to present in a later paper.

The tactual stimuli given by contact with the series of wires used for the electrical stimulus also served to guide the frogs.  They were accustomed to receive an electrical shock whenever they touched the wires on the blocked side of the entrance, hence on this side the tactual stimulus was the signal for a painful electrical stimulus.  When the animal chose the open passage it received the tactual stimulus just the same, but no shock followed.  After a few days’ experimentation it was noted that No. 2 frequently stopped as soon as it touched the wires, whether on the open or the closed side.  If on the closed side, it would usually turn almost immediately and by retracing its path escape by the open passage; if on the open side, it would sometimes turn about, but instead of going back over the course it had just taken, as on the other side, it would sit still for a few seconds, as if taking in the surroundings, then turn again and go on its way to the exit.  This whole reaction pointed to the formation of an association between the peculiar tactual sensation and the painful shock which frequently followed it.  Whenever the tactual stimulus came it was sufficient to check the