374 



the placing of lots of the same designation under approximately the same 

 experimental conditions are shown.* The mortality and failure data are 

 also given. 



The data were first brought into this form, and much of the material 

 used throughout the paper was drawn from these tables. In the appli- 

 cation of experimental results to the interpretation of actual weather 

 effects, velocity of development under diff'erent conditions is of first 

 importance. Velocity values may be determined in relative terms, with- 

 out reference to theoretical questions, from the reciprocals of the average 

 times (shown in the tables referred to) multiplied by some convenient 

 factor. The velocity values used in this paper were determined laigey 

 on that basis. 



Mortality and Failure to Pupati:. 



Mortality and failure to pupate have important relations to the 

 success of the species. Failure to pupate amounted to about 50 per cent 

 in the constant-temperature experiments taken as a whole. Cases in 

 which dormancy had begun in the autumn and in which it was not broken, 

 due to known lack of proper treatment, were entirely eliminated from 

 consideration. Only failures to pupate on the part of larvae of lots in 

 which other larvae did pupate were considered. However, in all of the 

 hibernated stock, incomplete hibernation changes were no doubt a factor 

 in failure to pupate. 



Mr. Glenn, in a personal communication, supplied data on mortality 

 in hibernation (Table XIV) which fall into two groups : In one group the 

 cocoons of the larvae were torn open in the spring for the purpose of 

 observing pupation, and in the other group they were undisturbed. Pos- 

 sibly some of the larvae included in these numbers may have died in the 

 fall before cold weather set in. The notes do not show this fact, but they 

 show the number of larvae which spun up in the cages in the fall of 1915 

 and 1916. The percentage of mortality of the hibernating generation of 

 1916-17 was less than that of 1915-16. Possibly this was partly due to 

 greater care in handling the hibernating generation in 1916-17, though 

 reasons are not evident. It could not have been due to the winter cold. 



• stocks I-V used in 1917-18 were as follows: I anri II were collected September 

 12 at Champaign : III. IV, and V were collected early in October a few miles south 

 of Sprin^eld, shipped to Champaign, and placed with the other stocks. All were 

 held at about 60° F. until Oct. 19 when I, II, and III were transferred to a temper- 

 ature varying from 28° to 38° F. and later transferred directly to the experimental 

 conditions without "freezing", in all probability, as the 28° temperatures were of 

 short duration. Stock IV was in similar conditions until Jan. 23 when it was put at 

 a constant temperature of 40° F. until experiments were started. Stock V was 

 "frozen" at 25° F. for 24 hours and transferred to the 40° constant temperature. 



All other stocks were merely stored at temperatures varying from 35° to 45° F. 

 Subsequent experience has shown that this is as important a period as any in the 

 life history ; and in future work, dates of collection, full control, and ful\ record of 

 all conditions must be kept. The work of Townsend shows the importance of this 

 period and indicates that all storage should be at or below 32° F. 



