ACCLIMATION IN PLANARIA DOROTOCEPHALA. 2Q7 



Few experiments with temperature changes in the opposite 

 direction acclimation temperature higher than testing tem- 

 perature were performed. The least satisfactory of these were 

 the "high-low" vs. "low-low" series. This was because it 

 required so long a time for the worms to show any appreciable 

 CO2 production that a new acclimation may have occurred or 

 at least begun to occur in that time. Series LXVI., I, "high- 

 low" for instance, showed no color change at all even in the con- 

 trols for more than 24 hours. As the previous experiments 

 had shown even a 1 2-hour period to permit of some degree of 

 acclimation, it is evident that in the above case we are dealing 

 with something in the nature of a second acclimation. This 

 difficulty could have been obviated by the use of greater numbers 

 of worms; but beyond a few experiments to illustrate this point, 

 no further attempts were made with this temperature combina- 

 tion. The two series "high-medium" vs. "medium-medium" 

 and "medium-low" vs. "low-low" showed in over 60 per cent, 

 of the cases that worms kept at a lower temperature have a 

 higher rate of COz production than those which have been 

 suddenly brought into that temperature from a higher one. 



Before leaving the subject of the indicator method, a few pre- 

 liminary attempts to check the short-time acclimation periods 

 may perhaps be mentioned. Though not conclusive on account 

 of their small number, they are at least suggestive. The experi- 

 mental procedure was as follows: Three lots of worms of as nearly 

 as possible equal weights were taken, two that had been at low 

 temperature, a third, the control, from medium temperature. 

 The heads from all three lots were cut off, but at such times that 

 one of the low temperature lots stood for a number of hours 

 12 to 24 headless before the experiment was begun; imme- 

 diately after decapitating, this lot was put into medium tempera- 

 ture, so that it had, each time, 12 to 24 hours in which to adjust 

 to that temperature before its rate of CO 2 production began to be 

 measured. This gave for comparison with the control, two lots 

 of the "low-medium" series, one of which was thus tested at 

 once at the time of change of temperature, the other only after 

 it had been given 12-24 hours in which to begin the process of 

 acclimation. From the previous experimental data with short- 



