Modification by Experience 227 



various observations, among others the fact that they ran all 

 over the passages in their earlier trials, so that smell might 

 have guided them wrong as well as right (385). This conclu- 

 sion was confirmed by the experiments of Watson, who found 

 that rats with the olfactory lobes removed learned the laby- 

 rinth as readily as normal rats (431). Yerkes, in his labyrinth 

 tests upon the crawfish and the frog, excluded smell as a means 

 of guidance by washing the labyrinth out between trials (454, 

 471). For certain species of ants, as we know, smell is the 

 dominant factor. Visual clews seem to be used by different 

 animals to different degrees. The frog displayed a disturb- 

 ance of its habit when red and white cards placed on either 

 side of the passage were interchanged (454). The crawfish 

 seemed to recognize and draw back from the screens in the 

 blind passage before running against them (471). The pigeons 

 tested by Rouse, when required to go through the labyrinth in 

 darkness, were obliged to relearn it, although they made the 

 first turn correctly. Perhaps, Rouse suggests, the stimulus to 

 the first turn was the sound of the door lifted to admit them, 

 or the touch of the narrow entrance (371). On the other 

 hand, Small found that altering the direction of the light had 

 little effect on the performances of his white rats. He also 

 placed wooden pegs painted red, at each division of the paths, 

 in the middle of the correct path, and caused the labyrinth 

 thus arranged to be learned by hitherto untrained rats. They 

 did not learn it any faster through the presence of these visual 

 hints, nor, when it had been learned, were they at all discom- 

 posed by the removal of the pegs (385). Allen's guinea pigs 

 did not alter their behavior with alteration of the position of 

 colored cards placed as guiding marks (4). And Watson's 

 blinded rats learned the labyrinth as readily as normal 

 ones (431). 



Rouse found that the pigeon could make use of auditory 



