Instinctive Behaviour of Crayfish 79 



thus liable to come in contact with floating 

 bodies, causing a discharge of some of the 

 potential energy of nerve cells of the brain, and 

 thus bringing about the contraction of the 

 muscles controlling the use of the animal's pre- 

 hensile organs. 



Professors Thorndike and Yerkes have done 

 much good work in testing the instinctive re- 

 actions of certain of the lower animals, by what 

 is known as the labyrinth method. This plan 

 consists in ascertaining the facility with which 

 an animal learns the correct road to take through 

 a labyrinth, interposed between its home and its 

 food. In the case of crayfish, a labyrinth offer- 

 ing only a single choice of passages was placed 

 between the animal's aquarium and its food. 

 " About half-way down the interposing box a 

 partition, put in longitudinally, divided it into 

 two passages, 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 per- 



