ACCLIMATION IN PLANARIA DOROTOCEPHALA. 



291 



of nos. I and 2 belonged to a series which had previously been 

 shifted several times from one temperature to another for very 

 short periods of time; the repeated changes may have been so 

 frequent as to check the effect of the last change. The result 

 of the last of these six exceptions (a little over 27 per cent, of the 

 total number of experiments), no. 10, can only be explained on the 

 ground of possible individual variation. 



Twenty-three experiments with temperature changes in the 

 opposite direction were performed. Table III. summarizes the 



TABLE III. 



Raised Temperature. 



Comparative Susceptibility. 



Experimental Lots. 



No. 



I 



2 



3 

 4 

 5 

 6 



7 

 8 



9 

 10 

 ii 

 12 

 13 

 14 

 15 

 16 



17 

 18 



19 



20 

 21 

 22 

 23 



Control Lots, 

 low-high 



low-medium 



medium-high 



low, 12 hrs. high 



12 hrs. " 



12 hrs. 



12 hrs. " 



12 hrs. " 



12 hrs. 



12 hrs. 



12 hrs. " 



12 hrs. " 



12 hrs. 



12 hrs. medium 



12 hrs. 



12 hrs. 



12 hrs. 



12 hrs. 



12 hrs. 



12 hrs. 

 < medium, 12 hrs. high 



12 hrs. 



12 hrs. " 



12 hrs. " 



12 hrs. " 

 > " 12 hrs. " 



results of such experiments. In these series the experimental 

 lots are brought into a temperature higher than that at which 

 they have been living and remain there 12 hours before deter- 

 mination of susceptibility is begun. The controls, as in Table II. 

 above, are brought into the second temperature (in this case the 

 higher one) only at the time when the determination of suscepti- 



