356 Eelation' of Water to the Behavior of 



covered with wire-netting. This dense growth produced horizontal zones with 

 atmospherical moisture, varying from high water-content at the bottom of the 

 cage to one of low content above the plants in the open. 



All beetle exposures and environmental measurements were made every 

 2 hours for a period of 12 observations at 3 strata within the cage, where insects 

 and instruments were exposed within wire-netting tubes, 30 cm. long and 

 5 cm. in diameter. Stratum A was 5 cm. above the ground near the base of the 

 potato plants, and contained the greatest moisture, thus giving the lowest 

 evaporation rate ; stratum B was 60 cm. above the ground, near the center of 

 the cage among the plants, and was directly above stratum A, so that it con- 

 tained less moisture, which gave a medium rate of evaporation ; while stratum 

 C was 90 cm. above ground and 5 cm. above the tops of the plants, and furnished 

 the driest conditions, with a high evaporation-rate, which was the only exposure 

 to true desert conditions. Each stratum was directly above the other, and all 

 exposures were made near the center of the cage. The environmental measure- 

 ments were obtained as follows: The evaporation rates, by using Livingston 

 atmometers ; relative humidities from wet and dry bulb readings ; temperatures, 

 from uniform standard centigrade thermometers. 



The environmental measurements were made every 2 hours for a period of 

 12 observations at the 3 strata within the experimental cage as previously 

 described and at the beginning of each period a new batch of beetles was 

 exposed to these conditions for 2 hours. The results are given in table 5. 



The beetles used in this experiment (Tucson A, g. II) were collected as soon 

 as possible after their emergence. Since these newly emerged individuals take 

 no food until after 24 hours, all collections were made previous to this time, so 

 that no error might be introduced in consequence of feeding ; moreover, no food 

 was given them at any time, and no excretion of waste products by the animals 

 was observed throughout the test. The beetles were placed at once in bell-jars 

 of uniform size in the constant-temperature room, which stood at 2-1° C, and 

 a high but uniform relative humidity was produced by placing wet filter-paper 

 inside the jars; this kept the air of the jars approximately saturated and the 

 beetles absorbed moisture until their reactions and physiological states were 

 uniform, as was proved by tests made later. 



The animals were retained in the jars until needed for further experiment. 

 Three batches of 10 beetles were removed from the constant-temperature room, 

 and exposed every 2 hours in wire-netting tubes, at the 3 strata within the cage. 

 Each batch was made up of similar stocks as follows : 4 individuals of 180 adults 

 which had emerged on July 5 were placed in the constant-temperature room at 

 8 a. m. July 6; 3 adults of 110 individuals which had emerged on July 6 were 

 also placed in this chamber on July 7 ; and 3 animals of 124 adults which had 

 emerged on July 7 were likewise placed in this room at 10 a. m. July 8 ; while a 

 batch of 30 beetles which emerged July 8 received the same treatment at 12 p. m. 

 July 8, and were used during the last 2 hours of the experiment, beginning at 

 4 p. m. on July 10. Thus all the organisms used were of the same culture and 

 of the same parents ; in general they were of the same age, and approximately 

 of similar states, so the conditions of the test were uniform. 



Aside from the environmental records, the following was also determined as 

 far as the insects were concerned : the total weight in grams of 10 beetles when 

 exposed, their weight in grams after 2 hours' exposure, the total grams of dry 



