ACCLIMATION IN PLANARIA DOROTOCEPHALA. 28 1 



30 C. For convenience these will be called "low," "medium" 

 and "high," and the exact temperatures given only when this 

 seems significant for the purpose of the experiment. Several 

 other terms used should be explained here. By "living" tem- 

 perature is meant, not the temperature of the natural environ- 

 ment, but that temperature at which they have been living 

 for a certain experimental period; in acclimation experiments 

 there is an "acclimation temperature." "Regulation tempera- 

 ture" means that temperature to which the worms are subjected 

 during regulation; similarly, "testing temperature" means the 

 temperature at which the metabolic condition of the worms is 

 tested. When two temperatures are given, the first is the living, 

 the second the testing or regulating temperature. 



The general methods employed in estimating the effect of 

 temperature upon the metabolism were: 



1. Susceptibility. 



2. Measurements of CO 2 production by 



1. Colorimetric method. 



2. The biometer. 



3. Rate of regulation and head-frequency. 



These methods will be described more fully as the experiments 

 are reported. 



III. GENERAL OBSERVATIONS. 



Even before any actual experiments are attempted, certain 

 general observations on the effect of temperature upon the worms 

 can be made. Out-of-door stock lives at a temperature of not 

 more than 8-14. Under these conditions the worms are not 

 very active, rather small but stocky, and of dark color. When 

 brought into the laboratory and kept there under temperature 

 conditions approximately like those out-of-doors they maintain 

 the same general appearance and are very sluggish even in 

 response to light. When kept at ordinary room temperature, 

 however, which during most seasons of the year represents a 

 rise of at least 7-8 C., the stock becomes more active and loses 

 some of its heavy pigmentation, changes which we have come to 

 associate with more rapid metabolism. Even if well fed the 

 worm shows these changes; and they are much more marked in 

 stock that is put at still higher temperature. At 27-30 C. 



