Glenn: Insect Development. 321 



celerate the rate of development. On this supposition 84, 85, 86, 

 87, 88 and 89 were taken in turn as the degree of the maximum rate 

 of development and the proper corrections made. This did not bring 

 the points back into line, as the points higher up still stood too far 

 to the right. It was then assumed, after a careful inspection of the 

 data, that temperatures above the degree of the maximum rate of 

 development not only did not accelerate but retarded the rate of 

 development in the same proportion as an equal fall in temperatures 

 below this point would retard it. 



On this supposition 84, 85, 86, 87, 88 and 89 degrees were in turn 

 taken as the degree of the maximum rate of development, and cor- 

 rections made in the location of the points in each case. It was 

 found that 87 degrees gave the best results. Points represented by 

 the crosses were then plotted, using the reciprocals of the periods 

 and the average daily temperatures above 52 degrees, diminished by 

 twice the average daily temperatures above 87 degrees. This 

 brought all the points nearly in line with the two original points 

 used in determining the line, indicating that the second supposition 

 relative to the effects of temperatures above the degree of the 

 maximum rate of development is correct and that 87 degrees is ap- 

 proximately the degree of the maximum rate of development. 



The corrections for temperatures above 87 degrees are entered in 

 column 8 and the corrected average effective temperatures (day- 

 degrees) are entered in column 9. 



The day-degree is used as the thermal unit and is equivalent to 

 a temperature of one degree lasting for one day. The product of 

 the day-degrees above 52 degrees (column 7) by the periods (column 

 4) are entered in column 10. It will be noted that they are nearly 

 constant for the lower temperature, but increase as the higher tem- 

 peratures are reached. 



The product of the day-degrees above 52 degrees diminished by 

 twice the day-degrees above 87 degrees (column 9) are recorded in 

 column 11. It will be seen that they are nearly constant for all 

 temperatures. 



The average of these products is 240. 



The formula is C = P (T — 2t') in which C = constant. P = pe- 

 riod in daj's, T = average day-degrees above 52 degrees and t = 

 average day-degrees above 87 degrees. This formula is the equation 

 of an hyperbola. Plotting the periods expressed in days against the 

 effective day-degrees (T — 2t'), we have the points as represented 



