38 



stretched skin is ruptured over the vertex of the head, and it is then 

 gradual!}^ cast off, revealing the delicate white pupa. The cast skin 

 frequently remains for some time attached to the tip of the abdomen. 



THE PUPA= 



When this stage is first entered the insect is a very delicate object 

 both in appearance and in realit3^ Its color is either pearly or cream 

 white. The sheaths for the adult appendages are fully formed at the 

 beginning of the stage and no subsequent changes are apparent except 

 in color (PI. IV, figs. 15 and 16). The eyes lirst become black, then 

 the proboscis, elj^tra, and femora become brownish and darker than 

 the other parts. 



The final molt requires about thirt}^ minutes. The skin splits open 

 over the front of the head and slips down along the proboscis and 

 back over the prothorax. The skin clings to the antennae 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 antennae are freed, and 

 finally the shrunken and crumpled old skin is kicked off the tip of 

 the abdomen by the hind legs. 



DURATION OF PUPAL STAGE, 



The duration of this stage is more easilj^ determined than that of any 

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

 pupae were allowed to remain in the squares or were removed there- 

 from. Considerable variation in the duration of this stage exists 

 among individuals 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 530 observations were made' 

 upon this point. Nearly ail of these are included in Table VI, which 

 shows a summary of the* results. 



Table Vl.— Tabular arrangemeat of observations upon the ditration of 2'>upcd stage in 



squares. 



Period of examination. 



Number 

 of obser- 

 vations. 



Range in 



duration 



of pupal 



stage. 



Average 

 duration 

 of stage. 



Average 

 effective 

 tempera- 

 ture. 



Total ef- 

 fective . 

 tempera- 

 ture. 



1902. 



Julj^ 6 to 31 



September 15 to October 3 . 

 September 24 to October 28 



November 2 to 13 



December 2 to 29 



1904. 



Experiments in ice box . . . 



Total 



161 

 81 



167 



29 



4 



530 



2 to 5 



3 to 7 



4 to 8 



5 to 6 

 10 to 16 



2 to 16 



3.5 

 5.2 

 6.0 

 5.6 

 14.5 



7.5 



39. 65 

 36.05 

 31.1 

 26.2 

 18. 55 



26.0 



138. 8 

 187. 5 

 185.1 

 146.7 

 269.0 



195.0 



