56 Journal of Comparative Neurology and Psychology. 



the series, counted. A crab going in and coming out again 

 was counted as in, but in every case by far the greater number 

 that had entered remained behind the screen as long as the food 

 was there. Two stimuh to two different senses, taste and vis- 

 ion were thus simultaneously and contiguously presented'; and 

 if this led to an association between the two "constructs," 

 "food" and "screen-darkness," it would necessitate the over- 

 ■cor)iing of the natural positive heliotropism manifested at the 

 start, and by contrast on this background the association would 

 stand out more prominently. After the crabs were fed each 



EXPERIMENT I. 



Lot 2, Eupagurus longicarpus. 



No. entering. Per cent. 

 3 lo 



14 46 



15 50 

 20 66-|- 

 25' 83 



27 90 

 26 96 



28 97 



' This long time was granted in order, if possible, that the crabs might 

 ultimately find their way in as a result, perhaps, of merely wandering around 

 in their evident endeavors to localize the source of the taste stimulus, which in 

 every case caused considerable agitation. The varying length of time used 

 throughout the series was a matter of best adapting the means to the end. Thus 

 it was quite justifiable to shorten the time later to 3' if the majority of the 

 crabs went through the openings in that time, although to do this would give 

 manifestly more favorable results than to wait longer. 



' On this 5th. as well as on each successive day up to the 9th. it was 

 noticed that as soon as the screen was put in, and the fish was placed behind it, 

 the crabs were much agitated and some started for the openings. 



3 The three that did not go in on the previous day had been remored for 

 the purpose of determining if possible if there was already a certain perma- 

 nency of habit among the twenty-seven entering; the result was confirmatory. 

 The three were then returned. 



* One had died. 



day under these conditions, fish and screen were removed, and 

 the latter was carefully washed with running sea water, as it 

 was also each time just before using. After a few days of this 

 treatment immediately upon the insertion of the screen the 



