The Potato Beetle in a Desert 375 



and Baker (1911) shows that snails during dry seasons form an epiphragm; 

 they usually bury themselves during hibernation and aestivation. On the other 

 hand, Pearl (1901) finds that the terrestrial slug Agriolimax can hibernate in 

 cold water. 



In the vertebrates, Rulot (1901) determines for the bat that the proportion 

 of water increases during hibernation from Xovember to April; but there 

 actually was a loss of water, more in proportion at the end than at the beginning. 

 Polimanti (190-1) finds that an increase in humidity increases the pounds in a 

 marmot during hibernation. 



In conclusion, the work of Sanderson (1908) agrees most closely with my 

 results upon hibernation. In discussing the relation of temperature to the 

 hibernation of insects, he states: 



" In come cases, however, the time of emergence from hibernation is con- 

 trolled by moisture conditions as well as temperature, or independent of tem- 

 perature. Thus Tower kept the potato beetle in hibernation for 18 months at a 

 high temperature but with a dry atmosphere, and they emerged as soon as 

 normal moisture conditions were produced. Webster and Hopkins have shown 

 a similar effect of the lack of rainfall on the emergence of the Hessian fly in the 

 fall. In relation to hibernation in humid climates the matter of moisture is 

 probably not a controlling factor, but undoubtedly has the most important 

 influence upon the time of emergence of forms in aestivation during the summer 

 or in an arid region." 



My results upon the potato-beetle substantiate the work of Sanderson. 



EFFECT OF CHANGES IN WATER-CONTENT UPON ALTERATIONS 

 IN TROPIC ACTIVITIES. 



The experiments and observations upon L. decemlineata proved that, when 

 surrounded by a moist medium, the beetles were positive to light and negative 

 to gravity. It is also evident from previous tests that if the moisture of the 

 surrounding medium was decreased, desiccation resulted, so that the insects 

 were reversed in their behavior and reacted negatively to light and positively to 

 gravity. These beetles, however, responded to any intensity of light if moved 

 from a lesser to a greater intensity, and accordingly when moved from darkness 

 into the moonlight at Tucson they always reacted ; and in many instances insects 

 which were negative to a strong light were also positive to a weak one. 



It was shown by Burdin (1913) that heat and dryness stimulate positive 

 reactions in terrestrial amphipods, while cold, moisture, and quiet favor nega- 

 tive reactions. The results of Dice (1914) prove that light of high intensity 

 makes daphnias positively geotropic, but a decrease in light intensity has the 

 reverse effect; and furthermore, these animals tend to become positively 

 geotropic in high temperatures and negatively geotropic in low. Kanda 

 (1916a), in studying geotropism in a marine snail, found that it is negatively 

 geotropic, but most individuals would orient positively if placed on a dry glass 

 or wooden plate. Later, Kanda (1916&) demonstrates for fresh-water snails 

 that they are negatively geotropic when their lungs are empty and positively 

 geotropic when their lungs are full of air. Olmsted (1917) finds that food is a 

 factor in the reversal of the behavior to gravity in Planaria maculata. Adams 

 (1903) concludes that earthworms retreat into their burrows during the day- 

 time because of their negative phototropism, but they emerge at night not so 



