Fig. 14. A sunny pool in Florida where mosquitoes 

 (Uranotaenia) breed. (Photo by R. H. Arnett, Jr.) 



ranges. As the radiant energy that is available on the surface of 

 the earth comes largely from the sun and, because of the rotation 

 of the earth on its axis, the supply varies regularly during every 

 twenty-four hours, the activities of many animals are rhythmic. 

 Nocturnal and diurnal animals have energy requirement levels 

 which are adjusted to particular periods in the diurnal cycle. Among 

 common pond fishes in the United States the carp and mud min- 

 now are most often active at night, the pumpkinseed during the day, 

 and the cisco at all hours. Most locusts sing during the day; katy- 

 dids and tree crickets, at night. Many cave anim.als live for genera- 

 tions without light. Even mammals, such as horses in mines, appear 

 to remain healthy for years in the absence of sunlight if fed proper 

 food. Many animals have periods of rest and activity which are 

 correlated with the changes in available energy which occur as the 

 earth travels annually about the sun; i.e., seasonal periodicities. 

 There are many examples of what are known as spring, summer, 



