Reactions of Isopods to Light 



267 



was evident almost immediately. After the lapse of thirteen 

 minutes, when the experiment was discontinued, the animals were 

 closely covered and left in darkness until the following day. 



The same animals were then experimented with under exactly 

 the same conditions as on the previous day, except that in the 

 meantime they had been m darkness for 16 hours, whereas on the 

 day before they had previously been exposed for a long time to 

 diffuse daylight. There was one other difference in the conditions 

 of the two experiments, but it was non-essential; in the first case 

 the animals were in the tank for only a short time before the experi- 

 ment began, whereas in the second case they had been in the tank 

 about 24 hours. Other experiments showed that this would, in 

 any case, influence only the time at which the reaction occurred 

 and that it would not affect the nature of the reaction. 



Table VI and the broken line of Fig. 4 show the results of this 

 experiment. 



TABLE VI 



AsELLUs COMMUNIS (i8 individuals) 

 December 13, 1906 

 Previous exposure: darkness {in tank) for 16 hours 

 Illumination: horizontal, 80 C. M.; lamp at Section-6 end 



+ I-5S 



