40 



THE AMERICAN NATURALIST 



[Vol. LIII 



1. Temperature. — That temperature affects profoundly 

 the daily life of the animal and limits its activities is 

 shown by the relation of daily variation in temperature 

 to the change from diurnal to crepuscular habit and to the 

 burrowing activities initiated by high or low tempera- 

 tures. Minimum temperature is probably associated 

 most closely with the phenomena of hibernation. Ac- 

 cording to Bachmetjew (1901) the minimum winter tem- 

 perature which can be survived by hibernating insects 

 depends on the degree of elimination of water from the 

 tissues and the consequent lowering of the freezing point 

 of the body fluids. Tower (1917) states that in the case 

 of potato beetles those animals acclimated to desert condi- 

 tions (retention of water) are killed at higher tempera- 

 tures than those of a more humid climate. In the experi- 

 ments to be described gradients in air temperature and in 

 soil temperature (substratum temperature) were estab- 

 lished and the reactions of animals in such gradients were 

 recorded. 



2. Wafer.— The water relation must always be impor- 

 tant ill an animal adapted to arid conditions, even though 

 this iclatioii may seem to be negative. As indicated by 

 tlic cxainitiatioii of excreta and observation of the water 

 relations of PUrynosoma it would appear that the ab- 

 sence of water as such would not have a limiting effect 

 on the distribution of the animals. It is probably neces- 

 sary, however, that a certain minimum amount of water 

 be supplied in the food, and that the evaporating power 

 of the air must not exceed a certain maximum for any 

 great length of time. It is to be doubted that any verte- 

 brate may subsist indefinitely witliont some small water 

 su]ip]y in addition to melabolic water. As shown in 

 pre\ion< expcriinent- (llM?*/). the reaction of Phryno- 

 .sown ill a u-radient of tlic rvaporal in.u' power of air is not 

 definite nide^^ tlu' ura.li^.nt ]h- v.m v <tee]). Dailv varia- 

 tion in the normal lial.itat v.m'v laruv. 



3. *So?7. — The ap]>ai-ent impoHance of tlie Inirrowing 

 reaction in the life history of tlie meml)ers of this genus 



