454 ^- ^'^- Bant, I 



ter. The dish was placed near the center oi the board and 8 cm. 

 from the place where the ball struck the board. In order to ob- 

 serve slight movements of Caecidotea during the tests, these ani- 

 mals, which are white, were placed in a dish the bottom of which 

 was black. For a similar reason the rather dark Asellus was ex- 

 perimented upon in a dish having a whitish bottom. In every 

 case the animals were allowed to remain from 15 minutes to an 

 hour in the dish to become accustomed to the new surroundings 

 before the experiments were begun and no animal was experi- 

 mented with until it had apparently begun to act and move nor- 

 mally after its transference. 



In these tests the following grades of stimuli were used. The 

 steel ball was dropped from 50 cm., 20 cm., 10 cm., 5 cm., and 2 

 cm., and had the following momenta at the instant of striking the 

 board: 1097, 694, 491, 347, and 219 C. G. S. units.'- 



In using the lead shot for the lower range of stimuli, it was 

 deemed advisable as a check to test the reactions of the animal 

 to vibrations produced by both the steel ball and the lead shot 

 when they collided with the board with the same momentum. 

 Hence the shot was dropped 83.6 cm. and the ball 2 cm., so that in 

 each case the bodies struck the board with a momentum of 219 

 C. D. S. units. The shot was used also from 50, 30, 20, 10 and 5 

 cm., producing momenta of 169, 131, 107, 76 and 54 C. G. S. units. 

 The whole series of momenta used then was (i) 1097, (2) 694, (3) 

 491, (4) 347, (5) 219 (steel ball), (6) 219 (shot), (7) 169, (8) 131, 

 (9) 107, ( 10) 76 and ( 11) 54 C. G. S. units. These will be referred 

 to in future as momenta of grades i to 1 1 respectivelv. In test- 

 ing an animal the greatest momentum was first used for 20 trials. 

 After each individual trial the result was recorded and the animal 

 allowed to come to rest again, if it had responded to the stimulus. 

 If the animal seemed erratic in any way, subsequent sets of 20 

 tests were made till constant results were obtained. After com- 



momentum = m v 



.'.momentum = m| 2sg 



m= mass, s= Jistance throuijh which tlic body falls, v = velocity, ami g = gravity. 



