HABIT FORMATION IN THE FIDDLER CRAB 227 



form, Carcinus granulatus, for habit formation. He constructed 

 a simple labyrinth containing two blind alleys and one opening. 

 In this labyrinth a number of crabs were liberated daily for a 

 period of two weeks, and were given on an average of four trials 

 per day. It was found that the animals gradually learned to 

 avoid the blind alleys, although even fifty experiences in the 

 case of most did not result in a perfect habit. He also found 

 that if the aquarium was divided into two compartments by 

 means of a wire screen, which contained an opening in its center, 

 the animals learned with increasing rapidity to find the opening, 

 in order to get to the food at the opposite side. From these 

 results Yerkes concluded that Carcinus possesses associative 

 memory. 



Yerkes and Huggins (1903) studied habit formation in the 

 crawfish, Cambarus affinis. They constructed a labyrinth con- 

 taining a triangular chamber at one end, while the opposite 

 end contained one closed and one open corner, the latter leading 

 into an aquarium. The animal was placed in the triangular 

 chamber, and could go to either corner in seeking to escape. 

 For one month, each of three animals was given on an average 

 two trials per day. The records of the movements to the closed 

 and open corners showed an increase from fifty to ninety per 

 cent in the direction which led to escape. A test of habit reten- 

 tion after a rest of two weeks, showed that the association 

 persisted. Their general conclusions are: (1) Crawfish are able 

 to learn a simple labyrinth habit, (2) they profit slowly, fifty 

 to a hundred experiences being necessary for perfect association, 

 (3) the chief factors in the habit forming process are smell, 

 touch, sight, and muscular activity, (4) if the possibility of 

 scent is excluded by washing the box after each trial, the animals 

 are still capable of learning. 



Other investigators working with different forms have con- 

 firmed Yerkes' conclusions. Spaulding (1904) found that the 

 hermit crab, Eupagurus longicarpus, which is positively photo- 

 tactic, could learn to go to a shaded portion of an aquarium 

 for food. The association became so perfect, that the mere 

 introduction of the screen, in order to divide the aquarium 

 into two compartments, caused the animals to run to the shaded 

 half. Drzewina (1908) observed that Pachygraspus marmoratus, 

 which is negatively phototactic during the day, reacts positively 



