36 



at the neck, the skin split along the back, and was then pushed down- 

 ward and backward along the venter of the larva. The cast head 

 shield remained attached to the rest of the skin. 



Immediately after casting the skin the head, as well as the rest of 

 the body of the larva, was of a pearly-white color. The tips of the 

 mandibles first became brown, and within a short time a 3^eIlowish 

 brown color marked the entire integument of the head. 



DURATION OF LARVAL STAGE. 



Most of the observations upon the larval stage were made between 

 September 1 and December 15, 1902. The temperature prevailing 

 during the first half of Septeniber was as high as is ordinarily experi- 

 enced at Victoria during midsummer, and therefore the extremes of 

 the average season may be considered as having been covered. 



The time of eg^ deposition was easily determined by exposing unin- 

 f ested squares in breeding cages containing active females. The time 

 of hatching of the larva could only be found by opening the square, 

 and it was so ascertained. The newl}^ hatched larva was then placed 

 in a small cavity made by lifting the covering on the side of a freshl}^ 

 picked square and removing one or two of the immature anthers. The 

 coverings were then replaced as carefull}^ as possible. Another dis- 

 turbance was necessary to determine exactly the date of pupation. 

 Observations made in this way were checked by others using larvae 

 which were allowed to go from egg deposition to pupation under nat- 

 ural conditions and without disturbance until the end of tKe larval 

 stage was approximately reached. Since the sum of the times found 

 for the various stages agrees approximately with the known duration 

 of the immature period in cases where no disturbance of normal con- 

 ditions occurred, we may conclude that the periods found for the larval 

 stage were approximately correct. 



Altogether 266 observations were recorded upon the duration of 

 this stage. The majority of the observations may be included in three 

 groups, and when thus grouped they may be best considered in rela- 

 tion to the effective temperature. Table V presents a brief summary 

 of these groups: 



Table V. — General results as to duration of larval stage in squares. 



Period of examination. 



1902, 



September 6 to October 5 



September 26 to October 21 



November 11 to December 12. . . 



1901. 

 Ice-box experiments 



Mean 

 average 

 tempera- 

 ture. 



78.7 

 73.6 

 62.5 



69.0 



Average 

 effective 

 tempera- 

 ture. 



°F. 

 35.7 

 30.6 

 19.5 



26.0 



Number 

 of obser- 

 vations. 



195 



15 



-15 



Average 



range of 



stage. 



Days. 



6 to 9 



7 to 12 

 20 to 30 



11 to 14 



