383 



95%. These classes were then treated as though all the experiments had 

 been run at the mean humidity for the group. It would have been desir- 

 able to keep the dilYerent generations separate, but this was impracticable 

 because of the small number of emerging moths. The results were segre- 

 gated according to humidity, regardless of generation or history. A few 

 discordant values shown in the tables were not used in the calculations. 



The relative velocities for each humidity were plotted on coordinate 

 paper. Since velocities for temperatures between 62° F. and 87° F. 

 usually fall into an approximately straight line, it was assumed that lines 

 drawn through these points crossed the temperature axis at a point 

 approximating the hyperbolic zero. These several approximate alpha 

 values were checked by Von Oettingen's method as in Table XVI, and in 

 some cases by the use of the formula as in Table XV. Each curve was 

 drawn through means of ordinates and abscissas of groups of points, and 

 to the best calculated alplia value. (Weighted means, taking into account 

 the number of individuals, were not used, because the stock was different 

 in history, and because the number of individuals put into the experiment 

 was different in practically every case.) 



270 

 Fig. 13 shows relative velocities -; plotted for each average- 

 days *" 



humidity group of pupae in the constant-temperature experiments. The 



curves are placed one above the other for convenience and indicate the 



geneiai form of the first rough curves which had been drawn. The scale 



at the left indicates the mean humidity for the data included in the curve, 



the base of each curve being on the mean humidity. The curves were 



first drawn, as shown by broken lines, for 95, 85. 73, 61, and 49 per cent 



humidity, and then harmonized as shown by the solid lines. The veloci- 



300 270 



ties had been originally plotted as — ; and were later changed to — ; 



days " days 



on the basis of the crucial experiments AD and AW with variable tem- 

 peratures (Table XVII, Fig. 15). The final survey of the entire 



relationship showed that the use of -5 would have properly compen- 

 sated for the retarding effect of constant-temperature conditions. The 

 use of these different factors does not change the relations of the relative 

 velocities in any way. It is perhaps impossible to be sure of the correct 

 factor to use in the early stages of a study. This final factor, 289, was 

 the average obtained by a recalculation of the data for all constant-tem- 

 perature experiments except five out of the fifty-five experiments, which 

 were rejected because they fell too far below the average. Only tempera- 

 tures between 62° and 89° F. were used in getting the average. A few 

 cases which appeared to have very rapid development, especially with a 

 combination of high humidities and rather high temperatures (which 

 seems to give greater variation than other combinations), were regarded 



