Reactions of I so pods 455 



pleting the tests with one momentum for an Asellus, the dish con- 

 taining the animal was gently removed from the table so as to be 

 beyond the influence of the vibrations, and the experiments were 

 repeated on a Caecidotea. This method of procedure was fol- 

 lowed for each pair of animals through all the eleven momenta 

 used. 



The kinds of reactions were designed by numbers as follows: 



o, no reaction. 



J, slight movements of anteniKt or other appendages. 



2, more extended movements of antennae or other appendages. 



^, movements of appendages and bending anterior end of body. 



^, same as "2" or "3" followed by the animal's crawling. 



5, crawling at once. 



For each test the number corresponding to the reaction was 

 recorded. Table V shows one of these records complete. 



Table V indicates that the responsiveness of this Asellus was 

 most pronounced to the vibrations produced b^' the falling bodies 

 striking the wood with 1097 and 694 C. G. S. units of momentum, 

 and that there was a rapid decrease as the lower momenta were 

 reached. With Gecidotea the reactions were most pronounced to 

 the higher momenta used and a rapid decrease in responsiveness 

 occurred with momenta below grade 4, but the responsiveness 

 is not entirely lost even with momenta of grade 11, only 54 

 C. G. S. units. Gecidotea responded not only more often but 

 with a greater vigor of reactions to all the grades of stimuli. 

 These two individuals are typical of the reaction of the two 

 species as Table VI will show. 



From Table VI Asellus is shown to be less reactive than Caeci- 

 dotea to this sort of stimulation. This difference appears not 

 only in the number of the responses, but in the vigor of the re- 

 sponses, and in the range of responsiveness, for Asellus is not 

 sensitive at all to such stimulation when the momentum is less 

 than 169 units, while C^ecidotea appears somewhat responsive to 

 as low a momentum as 54 units. Asellus gave the following aver- 



