286 A. M. Banta 



seldom failed to turn back into the dark region, unless they 

 crossed the plane in the middle of a run. It must not be thought, 

 however, from the above statement that an immediate turning 

 back into the dark region was the rule. For, in the first place, the 

 majority of the individuals crossed the plane without stopping at 

 all, and secondly, not more than one-fourth of those which 

 appeared to be stopped by the sudden illumination, turned directly 

 back. The sequence and character of the reactions at the plane 

 were by no means invariable. The animals, even when apparently 

 made to stop by the influence of the light, sometimes merely 

 waved the antennae somewhat, or lifted the head a little and 

 moved on in the same direction as before. Animals which the 

 sudden effect of the light did not cause to stop when going into the 

 illuminated area sometimes showed an immediate acceleration in 

 movement. If such acceleration in movement did not occur at 

 once it appeared very soon. The same statements may be made 

 with reference to those individuals which stopped at the plane 

 but did not find their way back into the dark region at once; 

 after the first pause they showed quickened movements either 

 at once or very soon thereafter. Hence, in any case, though the 

 animal might pause on first entering the illuminated region, 

 photokinetic effects very soon appeared. 



Of more general occurence than the stopping or turning back 

 of the animals upon entering the illuminated region was the stop- 

 ping of the animal just within the dark region when entering it 

 from the fight. It frequently happened that soon after starting 

 an experiment in which 25 or 30 Asellus were used, from four to 

 eight individuals at a time would be seen just within the dark 

 region, where they had stopped as soon as their impetus allowed 

 after passing beyond the reach of the light stimulus. 



No attempt was made to determine the reaction time at the 

 plane, but the distances beyond the plane of the positions at which 

 the animals stopped were apparently determined by the individ- 

 ual's reaction time and its momentum when it reached the plane. 



Occasionally the animals, after starting across the plane into 

 the dark region, would turn back into the illuminated region, but 

 this was exceptional. 



