Modification by Experience 273 



animals. Where a maze consists of only two passages, re- 

 quiring the animal to learn merely a single turning, the 

 method maybe practically merely a discrimination method : 

 thus Yerkes's (822) training of the earthworm made use of a 

 maze with two passages only to choose between, a light and 

 a dark one. In a pure maze experiment, however, there 

 is no way of distinguishing between the passages except 

 by experiencing the consequences of following them. Thus 

 the crayfish was tested by the use of a maze with a single 

 choice of paths. One end of the box communicated with 

 the aquarium ; about halfway down the length of the box 

 a partition put in longitudinally divided it into two pas- 

 sages, one of which was closed at the end by a glass plate. 

 In sixty trials the animals, which had originally chosen the 

 correct passage 50 per cent, of the time, came to choose it 

 90 per cent, of the time. A second series, with a single 

 animal upon which more tests a day were made, resulted 

 in the formation of a perfect habit in two hundred and fifty 

 experiments. The glass plate was then shifted to the other 

 passage, and the crayfish was naturally completely baffled 

 for a time, but succeeded in learning the new habit (829). 

 The crab Carcinus granulatus made progress in learning to 

 traverse a labyrinth with two points where a choice of path 

 had to be made, but did not wholly master it in fifty 

 trials (804). For both the crab and the crayfish, the 

 experience of getting back into the water was the influence 

 relied upon to eliminate the useless movements ; the slow 

 learning of these animals indicates that the method was not 

 well adapted to them. Ants showed some ability to learn 

 a maze with several turning points, following the proper 

 course even when their smell trail was obliterated (219). 

 Fish have proved able to learn very simple labyrinths, but 

 have not been tested in complicated ones (705, 121). 



