PAPERS ON ZOOLOGY 261 



the length of stages and the rate of development. Hu- 

 midity is one of these ; light, variability of temperature, 

 air movement and rate of evaporation are others. On 

 account of these complications it is necessary to express 

 rate of development in more than one dimension. In 

 1910, Ball writing in the Cairo Scientific Journal used 

 diagrams laid out on section paper in which he repre- 

 sented temperatures on the scale at the left and the 

 humidity on the horizontal scale at the top. He plotted 

 as points on this chart temperature and humidity for 

 each month in the year for various oases in the Sahara 

 and then connected the i3oints so plotted with straight 

 lines. (See Figure 2). Later Griffith Taylor (1914) of 

 Australia followed this same plan plotting the optimum 

 humidity and temperature for man on such a chart ac- 

 comi^anied by various similar plots for cities of the var- 

 ious parts of the world. He used wet bulb temperatures 

 which rendered his work not strictly comparable with 

 that of others. In 1916 Pierce applied this same princi- 

 ple to the Mexican Boll Weevil, but since he followed the 

 usual custom of the Bureau of Entomology in not cit- 

 ing any authorities, it is not possible to tell whether he 

 originated the idea independently also. 



In the case of humidity and temperature in our work 

 on the codlin moth we have found it possible to plot the 

 leng-th of the pupal period, the pupal mortahty, and the 

 failure to pupate in this fashion with advantageous re- 

 sults. The puj^al mortality is indicated at certain tem- 

 peratures and humidities in figure 3. Another type of 

 diagram is being prepared which we believe will prove 

 to be quite helpful in making predictions regarding the 

 time of appearance of the adult codlin moth. On this 

 diagram we are jDlotting for each temperature the per 

 cent deviation in the length of the pupal period due to 

 humidity, but the work is not complete. On a diagram 

 of this kind it is possible to plot also the march of tem- 

 perature and humidity for each day and thus determine 

 whether the humidities will have a marked effect on rate 

 of development or only a slight effect. Probably such 

 diagi-ams could be made for temperature and light, tem- 



