THE TEERAPIK SCALE. 



25 



larvae that have their anal plates adorned with major apical setae are 

 in the first instar. 



The growth is constant. Both length and width increase in the 

 same ratio. In the first instar the larvae increase their length and 

 width about two and one-half times, but they do not noticeably in- 

 crease their height. Tables XVIII and XIX show the measurements 

 for a total of 201 larvae at various ages during the first instar. The 

 data in Table XVIII are from larvae that emerged late in the season 

 of 1912. They encountered more than the usual amount of unfavor- 

 able weather. The data in Table XIX are from larvae that emerged 

 in July, 1913, and that had favorable conditions. This table also 

 shows the percentages in the first and second instars at various ages. 

 It required about 25 days for larvae emerging on August 9, 1912, to 

 reach their full development (0.9 to 1 mm. long) and to molt for the 

 first time, while those emerging July 1, 1913, reached this stage on 

 the sixteenth and seventeenth days. 



Table XVIII. — Measurements of 91 first-instar larvx during the unfavorable season of 



1912, Mont Alto, Pa. 



. No. 



Age. 



Number 

 of speci- 

 mens. 



Average 

 length. 



Average 

 width. 



Emerged— 



1 



Days. 



0.25 



5 



6 



7 



9 

 12 

 15 

 21 

 22 

 25 



6 

 5 

 3 

 2 



14 

 6 



24 



12 

 7 



12 



Mm. 



0.44 

 .5325 

 .555 

 .6046 

 .6307 

 .8407 

 . 8968 

 .931 

 .9348 

 .999 



Arm. 



0.23 

 . 2044 

 .287 

 .276 

 .279 

 .425 

 .439 

 .50 

 .499 

 .522 



Aug. 9 



2 



Do. 



3 



Do. 



4 



Do. 



5 



Do. 



6 



Do. 





Do. 



8 



Do. 



9 



Do. 



10 



Do. 







Total 





91 



















Table XIX. — Measurements of 110 first-instar larvx during the favorable season of 1913, 

 and the percentages of larvx on the trees in the first and second instars. 



No. 



Age. 



Number 

 of speci- 

 mens. 



Average 

 length. 



Average 

 width. 



Emerged— 



Per cent 

 of larva? 

 in first 

 instar. 



Per cent 



of larva? 



in second 



instar. 



1 



Days. 



3 



5 



8 



15 



17 



18 



19 



20 



21 



22 



23 



24 



22 

 21 

 15 

 19 

 8 

 10 

 5 

 3 

 3 

 3 

 1 



Mm. 

 0.5176 

 .555 

 .7275 

 .94725 

 .9625 

 .9975 

 .97 

 .9375 

 .9916 

 .925 

 .975 



Mm. 

 0.2659 

 .2873 

 .39 

 . 5235 

 .521875 

 .525 

 .52 

 .525 

 .5416 

 .525 

 .55 



July 17 



...do 



July 1 



...do 



...do 



...do 



...do 



June 26 

 July 1 

 Juno 24 

 Juno 26 

 July 1 



100 

 100 

 100 

 100 



80 



48 



20 



10.9 

 7 



10.7 

 3.2 





2 





3 









5 



20 



6.. 



52 





80 



8.. 



89.1 



9 



93 



10. 



89.3 



11 



96.8 



12 



100 















Total 





110 



























