112 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



unknown conditions of the physiological state of the organism. 

 But there is acting, if the first time the reactions A, B, and 

 C have answered to the stimulus a one after the other, and 

 if the second time C answers to it without any delay, it 

 being understood of course that it was C that had produced 

 a " liking " or had overcome a " disliking ' on the part of 

 the organism : that is what actually happens in Stentor, 

 and is very important as being a case of experience in a 

 simple motor act. Primitive forms of experience relating 

 to motorial combinations can be studied most advantageously 

 in Crustacea. In Yerkes's " labyrinth " experiment a crab 

 was placed in a box containing two different tracks, only 

 one of which led to the water. The crab ran at random 

 for a while, until at the end of many " trials " it found the 

 entrance to the water ; the second time the path to the 

 water was taken with much fewer mistakes, and at the end 

 of a set of experiments the crab ran to the water directly 

 without going wrong. Here we have a most typical case 

 of " experience " in which the " effect " of previous motor 

 stimuli is concerned, and it hardly matters at all, whether 

 we assume that the crab was guided by sight or that it was 

 guided by some spatial memory, unknown to us, such as we 

 have supposed to exist in some insects. Experience here 

 consisted in the omission of a set of previous reactions in 

 favour of the last effective one occurring in a series of con- 

 secutive stimulations. In another set of experiments carried 

 out by Spaulding the facts lay a little differently. A 

 hermit crab was fed with pieces of fish placed under a 

 green screen, and after a certain number of experiments it 

 ran beneath the green screen even if no piece was there. 

 Similar experiments have been carried out by the pupils of 



