420 



variable conditions, with mean temperature 69.5° and mean humidity 83 

 per cent, showing a rise of 18° F. at mid-day. the time was 14.7 days. 

 This decrease in velocity, correlated with the sharp mid-day rise followed 

 by a rapid return to normal, suggests acclimation, temperature regulation, 

 or a lag in the warming of the pupal body. No experiments with a sharp 

 fall in temperature followed by a quick return to normal have been tried. 



The effect of the normal daily variations of out-door temperatures, 

 when corrected to the velocity curve and compared to the constant-tem- 

 perature results, amounts to T-8 per cent more rapid development than 

 that under constant temperatures, for the pupae. The egg data suggest a 

 dift'erence of about 7 per cent, and the larval data about 8 per cent. In 

 every stage, development is more rapid under the normal out-door 

 variations. 



(b) The effect of rising or falling mean daily temperature is reflected 

 in the developmental total for the pupal stage and probably also for the 

 other stages. Fig. 28 shows rainfall, minimum and maximum tempera- 

 tures, and the relative rate of development for the groups of pupae, eggs, 

 and larvae indicated for 3 years, 101.5-17. A curve drawn so as to con- 

 nect the mean centers for the period covered by the thirty pupae from 

 pupation to emergence, rises and falls with the daily temperatures, sug- 

 gesting that rising temperatures retard development and falling tempera- 

 tures stimulate it. This may be explained on the basis of acclimation 

 (Jacobs '19). Presumably, the velocity of development does not increase 

 or decrease as rapidly as temperature changes. A close inspection of 

 Fig. 28 shows that, as a rule, when the number of rises in temperature 

 exceeds the number of drops, the developmental total is high, and vice 

 versa. There are some exceptions to this, but these are due to the 

 combining of several groups that pupated on different days. Taking 

 merely the groups that pupated on the same day, there is usually not very 

 much difference in time ; it appears that they string out when rising tem- 

 peratures come at the end. The correlation in general is good, but more 

 and detailed study will be necessary to make clear its exact meaning. 

 Doubtless direct measurement of CO., given off in relation to changes of 

 temperature would be significant. It is not clear but that phenomena 

 such as are shown by Lehenbauer ('14) may be the cause. He found 

 that the maximum rate in relation to temperature varies with the length 

 of exposure. 



(2.) Rainfall and Submergence in Water. (See Figs. 3 and 28.) 



During the "pre-pupal" period in hibernated larvae, submergence in 

 water appeared in some cases to have little or no effect, while in other 

 cases it accelerated development. Townsend has shown that submergence 

 must be frequent to have any effect. None of Glenn's larvae were sub- 

 merged or exposed to rain ; so, rainfall had only an indirect effect through 

 humidity. Hibernation in dry conditions lengthens the pupal period. This 

 is shown in the 1918 experiments and in Glenn's 1915 material after an 

 unusually dry late winter and early spring. The average time was nearly 



