5 8 Joitnial of Cojiiparative Neurology and Psycliology. ' 



further tested by simply putting in the screen with no fish be. 

 hind it, and the record of the crabs entering was taken in the 

 same way as before. The results are tabulated above. 



These results, if confirmed by control experiments, must, 

 we think, be accepted as showing conclusively that the Hermit 

 crab of the species lojigicarpus, firstly, forms an association be- 

 tween two sense-constructs, which, secondly, can be interpreted 

 as showing that the crab, subsequently, when only one stimulus 

 is presented, reproduces an image of the other. The same reac- 

 tion, entering the dark, which previously demanded two stimuli, 

 is later secured with only one stimulus ; the other therefore 

 must either be excited or reproduced. We may say perhaps 

 that if, when only the screen is put in as in the second series, 

 ofily visual perception or recognition takes place, then there is 

 no reason why the crabs should not remain where they are, in 

 the light, which is their natural preference. The screen, which 

 they now recognize, has however through association come to 

 mean for them other than something to be avoided ; it means 

 "food," and this meaning is present when the food is not. The 

 difference between Yerkes' experiments and these consists, 

 therefore, in this, that Yerkes' crabs "acquired the habit" of 

 going by a correct path from a place disliked to a place liked ; 

 the Hermits on the other hand go from a place liked to a place 

 naturally disliked, but "artificially" liked because of food either 

 there or — may we say — "expected" to be there. This must 

 mean that an associative element at first external, i. e., physical, 

 but now no longer that, is, nevertheless, now present as i?iter- 

 nal, and its internal presence must be due to either an excita- 

 tion or a reproduction by the other stimulus. If the latter, 

 then the Hermit may be said to remember vaguely, i. e. , to 

 7r const) uct. 



These conclusions are strengthened by the following con- 

 trol experiments : 



EXPERIMENT III. 



Lot 4. Aug. 20th. Forty crabs in a similar aquarium ; 

 the same screen was used, carefully washed each time. The 

 previous procedure was reversed here, by placing the crabs be- 



