27 



The final molt requires about thirty minutes. The skin splits open 

 over the front of the head and slijas down along tlie proboscis and 

 back over the prothorax; The skin clings to the antenna" and the tip 

 of the proboscis till after the dorsum has been uncovered and the legs 

 kicked free. Then by violently pulling upon the skin with the fore 

 legs first the tip of the snout and then the antennjB are freed, and 

 finally the shrunkeri and crumpled old skin is kicked off the tij) of 

 the abdomen bj^ the hind legs. 



LENGTH OF PUPAL STAGE. 



The length of this stage is more easily determined than that of any 

 other. It seemed to make little difference in the time whether the 

 pup?B were allowed to remain in the squares' or removed therefrom. 

 Considerable variation in the length of this stage exists among indi- 

 viduals of the same generation and even between offspring of the 

 same female and from eggs laid on the same day. The period of 

 investigation ranged from July to December, so that the extremes of 

 the season are included. Altogether over 450 observations were made 

 upon the length of this stage. Nearh^ all of these are included in 

 Table IV, which shows a summary of the results. 



Tabi.e IV. 



-Tabular arrangement of obsei'vat ions npon the lenytli of pfipal stage 

 in squares. 



Period of examination. 



1902. 

 JnlyOtoSl 



September 15 to October 3 . 

 September 24 to October 28 



November 2 to 13. 



December 2 to 29 



Numiber 

 of obser- 

 vations. 



161 

 81 



167 



29 



4 



Range in 



length 

 of pupal 



2 to 5 



3 to 7 



4 to 8 



5 to 6 

 10 to 16 



Average 



length 



of stage. 



Average 

 effective 

 tempera- 

 ture. 



Days. 

 3.5 

 5.2 

 6.0 

 5.6 

 14.5 



°F. 

 39. &5 

 36.05 

 31.1 

 26.2 

 18.55 



It should be noted in connection with Table IV that the observa- 

 tions made in November were during a period of rather warih weather 

 and that tlie temperature records for that time are incomj)lete. It is 

 likely that the average effective temperature given for that period 

 might be different were the records complete. 



The average length of this period during hot weather is from three 

 to four days, and the period increases as the cool fall weather 

 approaches to a maximum of about fifteen da3\s. 



A comparison of Tables I, III, and IV shows that the decrease in 

 temperature affects each stage in veiy nearly the same proportion. 

 In each case the maximum recorded length of any stage is about four 

 times its minimum, and the great retardation in each case occurs 

 somewhere between 60° and 70° F. of mean average temperature, or 

 17° to 27° F. of effective temiierature. Even greater retardation 

 occurs during the winter season. 



