65 



con.se(iuenth\ the period>s during- which greatest injiiiT is done. Deter- 

 minations of this character were made in connection with the previ- 

 ously mentioned ])reeding work. 



Measurements made of the length of the bod}^ are of but little use, 

 since the}^ ma}^ be varied so much b}- the movements of the larva. 

 There is a rather constant and gradual increase, however, from birth 

 to maturit3^ as shown by the measurements given below, which are 

 averages of twent3"-tive larvae. 



Table XX. — Showing amount of growth during, amJ lengtli at end of, each instar. 



Instar. 



Amount 

 of growth 

 during 

 each in- 

 star. 



Length at 

 end of 

 each in- 

 star. 



I 



II 



Ill 



IV 



V 



VI 



mm. \ mm. 

 2.02 t 3.52 

 2.65 1 6.17 

 4. 53 ! • 10. 70 

 7.68 18.58 

 10.51 29.39 

 13.35 ' 42.74 



Thus it will be noticed that a larva shows 

 a greater amount of growth during each 

 succeeding larval instar. This is shoA^n 

 graphically in the accompanving curve 

 (fig. 6). 



More accurate measurements are those 

 based upon the size of the head, which does 

 not change between the molts, and thus 

 serves b}^ its almost constant size to identify 

 the instar of any given larva. By meas- 

 uring large numbers of head casts thrown 

 off at the molts, it was found that they are 

 fairh^ constant for each instar, sufficiently so 

 to enable one to tell the stage of any larva 

 positiveh\ The following table is compiled 

 from measurements of over one hundred 

 specimens: 



I II III IV V VI 



Fig. 6. —Diagrammatic represen- 

 tation of comparative rate of 

 growth of larvae during dif- 

 ferent instars (original;. 



Table XXI. — Showing average width of head casts for respective larval instars. 



Width and range. 



Stagel. 



Stage II. 



Stage III. 



Stage IV. 



Stage V. 



Stage VI. 



Width 



mm. 

 0.30 



(«) 



mm. 

 0.48 

 0.42-0.54 



■ 



mm. 

 0.78 

 0. 67-1. 00 



mm. 

 1.33 

 1.21-1.50 



mjii. 

 2.05 

 1. 73-2. 28 



mm. 

 3 95 



Kange 



2 85-5 00 







a Practically constant. 



