Reactions of I so pods 461 



^. With Vibrations, lOO per Second 



A fourth method of testing the relative responsiveness of these 

 two species to mechanical stimulation was by means of an elec- 

 tric tuning fork whose rate was 100 complete vibrations per sec- 

 ond. The animals, as in previous experiments were placed in 

 small stentor dishes, the Asellus over a light-colored bottom and 

 the Caecidotea over a black one. The stentor dish containing 

 the animal was placed upon a heavy block of hard pine wood 

 41 cm. long, 22 cm. broad and 11 cm. thick, with planed sur- 

 faces. The dish was firmly fixed upon the block near one end by- 

 being clamped between three nails driven partly into the block. 

 The block rested upon a pile of crumpled paper two inches thick 

 placed upon a table whose legs rested upon crumpled paper. Close 

 by the first table was a second one likewise supported on paper, 

 and upon this table lay the fork, also on a thick pad of paper. 

 The piles of paper prevented any perceptible transmission of 

 the vibrations (other than when desired) from the fork to the 

 stentor dish in which the animal was confined. The fork was 

 driven by a Columbia No. 6 dry cell and a simple key was used 

 to make and break the circuit as desired. Two cells were used 

 alternately to avoid the effects of running down. 



The manner of experimentation was as follows: The animal 

 to be tested was allowed to remain in the stentor dish in position 

 for a sufficient length of time to become thoroughly settled, after 

 which the fork was set in vibration and slipped over its support 

 of paper (upon which rested a smooth sheet of glass) until its 

 base came into firm contact with the end of the block on which 

 the stentor dish rested. After a momentary contact the fork 

 was withdrawn and a record of the response of the animal, if 

 any was made. The test was repeated after about ten seconds 

 or more. Twenty of these tests were made upon each individual, 

 first as Asellus then a Caecidotea, until 15 pairs of individuals 

 had been tested. The responses were ranked, as in the experi- 

 ments on the effect of stimulation by the concussions of falling 

 balls (see p. 453), though it was found expedient to add another 

 class. Sometimes the animals moved just at the instant before 



