jNIoori: and Hiwckkford: Water Insects. 411 



gress swiftly through early life stages toward the vigor of mid- 

 summer maturity, is to retard or to inhibit the development of life. 

 Seeds may germinate, but, without rains, growth lags or ceases. 

 Larva) of insects, polliwogs, and whatever animal life is dependent 

 on waters, are restricted to permanent pools, springs or streams, for 

 there are no temporary breeding waters in the dryness of the spring. 

 The distribution of the yearly precipitation at four stations in the 

 vicinity of the localities described in this paper, is shown in chart 

 on page 412. 



The temperature of the plateaus is influenced to a large extent 

 by the clear, dry atmosphere and by the altitude. During the days 

 the sun warms the air and the ground, and the bare rocks reflect 

 the heat rays back into the air. At night radiation is rapid and the 

 temperature quickly falls. This large diurnal range in temperature 

 is characteristic of arid or semiarid regions. At Tropic, in central 

 western Garfield county, a freezing temperature in each of the 

 twelve months has been reported, while the maximum temperature 

 is greater than 100 degrees. (See chart, page 413.) 



