408 



was collected, beginning August 16th and running through September 

 28th. They were kept at a temperature of 70° F. and humidity of 

 approximately 45 per cent until September 23d ; between this date and 

 October 23d the temperature was lowered at 50° by steps, first falling to 

 59° only at night, and then being lowered to a constant 50° on October 

 8th, and finally to 50° on October 23d. A temperature between 50° and 

 52° was maintained until December 27'th, when it was lowered to 37° and 

 held between 35° and 37° until February 14th, when it was gradually 

 raised to 48°, and on March 15th, to 72°. The larvae were then kept at 

 72° F. and 85 per cent humidity for observation as to time of pupation 

 and emergence. Owing to apparent discrepancies in the time of pupation 

 recorded by the assistant in charge of daily observations of this experi- 

 ment, it was deemed best to use only the time of emergence, concerning 

 which there was no doubt. Fig. 25 shows the distribution of emergence 

 in May, 1921. The number of times the groups had spun cocoons, the 

 dates of collection, and the relative humidities are indicated in the margin 

 of Part A of Fig. 25. 



There is apparently no consistency in the different numbers of times 

 which the cocoons were spun in the sets of the same humidity and collect- 

 ing date, nor is there any consistent relation to the moisture treatment 

 during the hibernation period in this experiment. (Fig. 25.) The earliest^ 

 individuals to appear are by no means consistently from either the "wet" 

 or "dry" lots. The lots labelled "W" had been stored at humidities of 

 100 per cent and submerged in water once a month long enough to 

 saturate the pasteboards and surround the cocoons with water. Those 

 labelled "D" had been stored at 90 per cent humidity but had not been 

 submerged at all. The lack of results from this submergence has been 

 shown by Townsend to be due to the infrequency of the wetting. (There 

 is an essential diflference in the times of emergence if rainfall is heavy.) 



The three emergence groups, when added together (Fig. 25B) and 

 compared with Glenn's data on emergence, show main maxima corre- 

 sponding with his main maxima ; and an explanation of the variation in 

 the time required to overcome dormancy (variations in the pupal stage 

 are of a different nature) must be sought in other causes, such as heredity, 

 conditions of the food supply, or weather conditions during autumn. 



Field observers have stated that the initiation of dormancy in summer 

 and autumn larvae is due to a temperature of 50° F. or thereabout. Two 

 hundred and five larvae were collected in the summer of 1920 between 

 July 22 and August 14 and subjected to temperatures varying from 39° 

 to 54° F. These larvae were divided into four classes: (a) pupating, 

 (b) failing to pupate, (c) escaping from the corrugated pasteboards. 

 and (d) dying. Those dying and escaping were ignored; only those 

 remaining alive in the pasteboards were considered as having been experi- 

 mented upon. After those dying and those escaping were deducted, the 



