Spaulding, Association in Hermit Crabs. 55. 



cleaned Fiindidns held in place on a wire. The same portion 

 of the aquarium was darkened each time just before feeding by 

 setting down into the constantly running water a screen consist- 

 ing of two thin boards fastened at right angles, leaving only an 

 opening at each end of the vertical board wide enough for the 

 crabs to go through one by one ; around the outside of the 

 aquarium from end to end of this portion set off by the screen 

 was kept a piece of heavy brown paper to shut out the light 

 coming from the other direction. The only light which could 

 enter came therefore through the openings at each end. Sand 

 was placed in the bottom of the aquarium, and all the condi- 

 tions such as its position and that of the tap, with the exception 

 of the putting in and taking out of the wooden screen, were 

 kept constant during the entire series of experiments. 



These were conducted in detail as follows : to establish, 

 first, an association and, second, present an occasion for possible 

 "reproduction" from the "after-effect" of one by the external 

 stimulus of the other "construct." 



Thirty-six crabs of the species Eiipagiirus longicarpus were 

 placed in the aquarium on July 30th, and, first, allowed until 

 August 6th to become accustomed to aquarium conditions ;. 

 during this period they were simply fed each day with a fresh 

 FunduluSy no screen being used ; they seized their food most 

 eagerly, oftentimes fighting and driving each other away from 

 it. The death of six selected the thirty most fit individuals. 

 The crabs were, furthermore, observed to remain in the lightest 

 part of the aquarium practically all of the time, i. e., they 

 were positively heliotropic. The positive heliotropism was con- 

 firmed by a number of control experiments with other lots and 

 by that of Aug. 6th. The screen was inserted and all the crabs, 

 30 in number, placed behind it In 10 minutes 28 had gone 

 through the opening into the light and 27 of these were near 

 the point of its maximum intensity. 



Each day following this, the screen was inserted, a fish on 

 a wire placed in the darkened portion, and the number of crabs 

 going into the dark through either one of the entrances at the 

 end within a given time, which was constantly shortened during 



