IWAHARA (1) has shown that spontaneous alternation in a simple T-maze in Armadillidium vulgare is little affected by intertrial intervals (0″and 120″) and that the running time in the maze is also not significantly different whether trials are massed or spaced. Thus it was reasoned that the nonsignificant effect of intertrial interval upon alternation may be due to the fact that the accumulation of reactive inhibition which is supposed to affect alternation, is relatively independent of massing of the trials in this animal.The purpose of the present study is to repeat the IWAHARA study with broader variations of intertrial intervals, with more extended trials and, in addition, with three different levels of illumination. In Experiment I six groups of 17 animals each were run on a factorial design with 0″, 120″, and 300″intertrial intervals, and two levels of illumination (250 lux and less than 1 lux). Two groups with a 0″-interval were given 30 trials, while other four groups 20 trials. In Experiment II two groups were run only twice with a 24 hour-interval one under light and another under dark illumination. In Experiment III was run another group with a 120″-interval from the light starting point to the dark goal. No particular reinforcement was given.The results were: (1) spontaneous alternation (about 40%) was again little affected by intertrial intervals whether alternation was computed on the first two trials or on the total trials, and it was independent of an increase of trial numbers, (2) the animal ran faster with massed trials but slower with an increase of trials, and under the dark illumination, (3) it was fastest with the dark goal, (4) running time was not significantly different whether the animal alternated or repeated the preceding responses, and finally (5) significant individual differences were found with respect to position preferences and running time but not with respect to spontaneous alternation. The results were discussed in connection with previous studies.