ACCLIMATION IN PLANARIA DOROTOCEPHALA. 



289 



twelve hours in a different temperature; the susceptibility to 

 cyanide was then compared at the second temperature with 

 that of worms from the same stock which had not been exposed 

 to the second temperature until the time of testing. Both lots 

 were tested at the second temperature. If the worms show 

 consistently different death rates it will be proof that time in- 

 tervals as short as these few hours actually produce persistent 

 modifications in metabolism. The results are more easily tabu- 

 lated and considered in separate groups according to the direction 

 of the temperature change. 



In Table II. the experimental lots are brought into a tempera- 



TABLE II. 



Lowered Temperature. 



Comparative Susceptibility. 

 No. Control Lots. Experimental Lots. 



1 high-low high, 12 hrs. low 



2 12 hrs. 



3 12 hrs. " 



4 12 hrs. " 



5 12 hrs. " 



6 < 12 hr,. " 



7 " 12 hrs. " 



8 12 hrs. " 



9 < 12 hrs. " 



10 12 hrs. 



11 12 hrs. " 



12 high-medium < 12 hrs. medium 



13 12 hrs. 



14 12 hrs. 



15 12 hrs. 



16 medium-low < medium, 12 hrs. low 



17 12 hrs. " 



18 12 hrs. " 



19 12 hrs. " 



20 12 hrs. " 



21 12 hrs. " 



22 < 12 hrs. " 



ture below that at which they have been living and remain there 

 12 hours before determination of their susceptibility is begun. 

 The control lots, on the other hand, are brought into the lower 

 temperature only when the determination of susceptibility begins. 

 The table shows the difference in susceptibility between such 



