REACTIONS OF LAND ISOPODS TO LIGHT 



221 



TABLE 6 

 Results of experiments testing the influence of repeated stinmlation on Oniscus. 

 The animals were facing the light in all instances. Intensity 12.955 CM. 



1 The numbers in this column diminish, because the tests of only four indi- 

 viduals were continued through GO stimuli, others extending only to 40, 30, and 20. 



The results were compiled by dividing the responses into 

 groups of ten successive responses and measuring the average 

 angle of negativeness. 



Table 6, which summarizes the reactions of these sixteen ani- 

 mals, shows no influence of repetition upon the character of the 

 response. 



The average turning from the light was as definite after sixty 

 successive stimuli as at first. 



Whatever effect was caused by the delay is shown by a lessen- 

 ing of activity as is indicated by the interval before response, 

 shown in the last column of table 6. The figures are only ap- 

 proximate, as all delays over 60 seconds were counted as 60 

 seconds in making the averages. The essential conclusion is 

 that after the first few trials there is usually a slight decrease 

 in responsiveness, but from that time on there is little change. 

 The delay is probably due chiefly to the effects of handling, as a 

 sunilar delay occurs just as readily when the animals are moved 

 about on the table by the same method of manipulation, but not 

 exposed to fight atr all. 



Furthermore, while there were changes in individual behavior 

 which are not shown in the above table, there was no consistent 

 change in phototaxis which could be traced to the effects of repe- 

 tition. In some individuals the angle of negativeness decreased 

 with continued stimulation, in others it increased, while in still 

 others it passed through both of these variations successively. 



THE JOURNAL OF EXPERIMENTAL ZOSLOGY, VOL. 27, NO. 2 



