26 



BULLETIN 351, U. S. DEPARTMENT OF AGEICULTURE. 



The second column in each table gives the age in days. This is 

 calculated from the time the larvse loft the brood chamber. The 

 sixth column gives the date upon which the specimens emerged. 

 There are added to Table XIX two columns of data to show the 

 percentages of larvae in the first instar and second instar at different 

 age^s. An examination of these columns will show that 50 per cent 

 of the larvse had passed from the first to the second instar upon the 





A GC /N DA YS 



/ 



.9 

 .8 



k 



.s 



.4^ 







































.9 



97 



5 









.9 



99 

































y. 



y 



o 



?6 



as 





o.. 



39 



97 



1 

 5?' 

































/ 



/ 



94 



72 



^ « 





93 



.9 



3/ 



o. 



sa 



5 



























/ 



/ 



* 

 * 



• 

 • 



-»: 



39 



68 







































/ 



1 

 1 



. 



S4 



67 











































l\ 





1 



1 

 1 











































.7 



?7 



sj 



^ 



• » 













































> 



f 





t 



f 













































/ 



/ 



» 



1 



so 



^3 

 <^6 



or 





































.5 



55 



J 



1 



'55 



f 



5 









































SI 



76 



/ 



ou 



53 



25 









































y 



/. 



r 



* 



9 

















































^4 



^. 



















































Fig. 8. — Growth curves for the first instar of the terrapin scale. (Original.) 



eighteenth day, and that all had left the first instar by the twenty- 

 fourth day. Eighteen days is the normal time spent in the first 

 instar by larvae during favorable seasons. Figure 8 shows the deflec- 

 tion of the growth curve for larvae in the first instar which resulted 

 from the late emergence during the unfavorable season of 1912, as 

 compared with the curve for the favorable season of 1913. These 

 curves are derived from the data in Tables XVIII and XIX. The 

 curves are similar, but the broken curve shows clearly the effect of 

 unfavorable weather in 1912 at both the beginning and the end of 

 the instar. 



