380 Eelation of Watek to the Behavior of 



It is not true that all animals do absorb water, for my experiments upon the 

 scorpion and horned lizard (Phrynosoma cornutum) of the Tucson Desert indi- 

 cated that these animals would not imbide any aerial water, and even when 

 immersed in it no absorption was detected; furthermore, when desiccated no 

 difference in weight was observed. A large scorpion lived for more than 2 

 months in a desiccator without food, but it probably died of starvation. If 

 lizards do not absorb any appreciable amount of water or lose any through 

 desiccation, then such a condition might demonstrate why they are distributed 

 in a desert as well as in a hot humid region ; therefore, the water-relation would 

 not be the determining factor in a lizard's habitat, but the temperature-relation 

 should be of greater importance in determining its distribution. This might 

 also account for the results of Weese (1917), since he studied the reactions of 

 the horned lizard to evaporation and temperature gradients, but found that the 

 lizard responded definitely to temperature, while there was no marked reaction 

 to evaporation. In this connection the work of Matthews (1913) is important. 

 He says : 



" There is a mechanism for rendering mammals tolerably independent of the 

 moisture content of their environment, a mechanism most highly developed in 

 the reptiles. A mechanism formed by the replacing of the wet skin of the 

 amphibian by a dry or scaly skin; the perfecting of the kidneys to maintain 

 osmotic pressure of the blood ; the control of the sweat glands and loss of water 

 by the intestines ; the development of membranes non-permeable to salts so that 



animals may sit in fresh water and lose their salts By this improvement 



reptiles have secured almost complete independence of the water-content of 

 their surroundings." 



Water is essential to life, says Babcock (1912), for during the period of 

 development it is the most abundant constituent of living organisms. He 

 continues : 



" Some of this water is imbibed directly, some of it is taken with solid food 

 which is rarely dry, and some of it is formed within the organisms by metabolic 

 changes in the organic constituents of the food and tissues, induced by respira- 

 tion and other vital processes. The relative amount of water derived from each 

 of these sources depends upon the kind of organisms, its period of growth, the 

 nature of its food, its environment, and its activities." 



His experiments show that many varieties of insects, such as the clothes-moth, 

 the bee-moth, and the flour-beetle, the flour-moth, and others live during all 

 stages of development upon foods containing less than 10 per cent of water. 

 He concludes that nearly all the water used by insects feeding upon air-dried 

 foods is metabolic. In my own experiments upon the potato-beetle and other 

 animals there are no data upon metabolic water and its relation to behavior. 



The results of Hegner (1916) further illustrate the water-relation in animals. 

 He arranged an experiment upon oviposition in the potato-beetle, so that 35 

 batches of eggs were in the sunlight and 15 were in the shade. Those in the sun 

 came to nothing, but all in the shade were hatched. It was found that develop- 

 ment had started in the sunlight, but that desiccation probably arrested this 

 process; therefore he concludes that the advantage of concealment is not so 

 great as that secured by shielding the eggs from the desiccating properties of the 

 sun. My results show that the majority of adults orient to gravity with their 

 dorsal side down, which might explain why eggs are usually deposited on the 

 under side of a potato-leaf. 



