256 BEHAVIOR OF THE LOWER ORGANISMS 



the partition was placed in the right passageway, as in Fig. 139. The 

 crayfish which turned to the left on leaving T escaped at once to the water. 

 But if it turned to the right it passed into the pocket G, and was compelled 

 to explore the region, finally turning to the left and passing the partition 

 P, before it could escape. Three individuals were given sixty trials each 

 in the course of thirty days. In the first ten trials they went just as fre- 

 quently into the blind passage as toward the water. In the second ten 

 trials, the animals started in 60 per cent of the cases toward the open 

 passage at the left. In the next ten trials this proportion had risen to 

 75.8 per cent; in the following ten, to 83.3 per cent. In the last ten 

 trials of the sixty, very few mistakes were made. In 90 per cent of all 

 cases they went straight for the open passage. In another series of 

 experiments an individual, after four hundred trials, made only one 

 mistake in fifty trials. Similar results were obtained by Yerkes (1902) 

 in experimenting on the crab Carcinus granulatus. 



Thus at the beginning of the experiment the animals were as likely 

 to go to the right as to the left, while at the end they went almost inva- 

 riably to the left. Since the external conditions had not changed, the 

 animals themselves must have changed. Their internal condition now 

 differed in some way from the original condition. 



Yerkes and Huggins (1903) endeavored to determine how easily 

 this acquired condition could be modified or destroyed. After the cray- 

 fish had learned to go through the open passageway so as to make a mis- 

 take in only one case in ten, the experiments were discontinued for two 

 weeks. On the fourteenth day the animals were still inclined to go 

 straight to the open passage, though the habit had become dulled, and 

 they now made mistakes in about three cases out of ten. 



In other experiments, after the animals had acquired the habit of 

 escaping through the right passage, the partition G was changed, so as to 



block up this passage, but 

 leave the left one open. 

 At the next trial the ani- 

 mal made a long-continued 

 attempt to escape by the 

 right-hand passageway, fol- 

 lowing the path shown in 



Fig. 140. — Path followed by a crayfish which has Yw IJ.O It Wandered 



formed the habit of escaping to the water by the right- & " 



hand passageway, when this passage is closed and the about tor utteeil minutes 



left one opened. After Yerkes and Huggins. before disCOVCrino" the Open 



way. But in the next trial it turned to the left, and thereafter it 

 turned almost as regularly to the left as it had before turned to the 

 right. 



