166 CLYDE C. HAMILTON. 



larva at a temperature of 20.5 C. The distance from the right 

 to left represents the length of the cage and the vertical distance 

 time. Graph 8 shows the control of another Evarthrus sodalis 

 larva with a temperature of 23 C. at the start and 26.5 C. at 

 the end. 



B. Reaction in Evaporation and Temperature Gradients. The 

 experiments on evaporation were varied by changing the relative 

 humidity, the temperature, and the rate of air flow. The flow 

 of air used, unless otherwise stated, was 13.3 liters per minute. 

 This volume of air was secured by using a diaphragm with an 

 opening five sixteenths of an inch in diameter and a displacement 

 of three millimeters of water. 



Graph 2 shows the reaction of two Evarthrus sodalis larvae to 

 dry air at a temperature of 21 C. The avoidance of the dry 

 air was very sharp and decided by one of them. The other 

 larva rushed into the dry air, was soon overcome and was unable 

 to get out. It squirmed and rolled about, became less active and 

 was dead at the end of forty minutes. It had shrunken consider- 

 ably, due to the withdrawal of water, and had turned a dirty 

 yellow color. The larva which avoided the dry air was appar- 

 ently as active at the end of the experiment as at the beginning. 

 At lower temperatures the larvae were generally not so active and 

 did not avoid the dry air so sharply. Graph 3 shows the reaction 

 of an Evarthrus sodalis larva to dry air at a temperature of 17 C. 

 In the wet air it acted normal, except for some sluggishness. In 

 the medium and dry air it squirmed and rolled about but was not 

 affected as much as when the temperature was higher. Graph 

 4 shows the reaction of an Evarthrus sodalis larva, which had been 

 outside in freezing weather for five days, to a high temperature 

 and a low percentage of moisture. The behavior was different 

 from those in dry air at lower temperatures in that the larva 

 was sluggish, depressed and appeared fatigued. The effect 

 appeared to be very similar to that of carbon dioxide, which will 

 be described later. The graph shows the movement of the larva 

 for forty minutes, the second twenty minutes starting at (X). 

 At the end of the forty minutes the larva was considerably 

 shrunken, was a creamy yellow color in the membranous areas, 

 and appeared to be dead. It began to revive in a little over an 



