THE TERRAPIN" SCALE. 



35 



During the migration of the rearing of July 22 the maximum daily 

 temperature rose gradually from 73° F. on August 28 to 85° F. upon 

 September 1, after which it fell to 74° F. upon September 3, and 

 then rose abruptly to 90° F. upon September 6. It then dropped 

 to 67° F. upon September 12. The average daily temperature 

 remained nearly constant at 66° F. from August 28 to August 31, 





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Fig. 11.— Curve of the twigward migration of the terrapin scale for a rearing that emerged August 9, 1912. 



(Original.) 



when it rose abruptly to 73° F. upon September 1. During Sep- 

 tember 2 and 3 it made a gradual drop to 68° F., and then rose in a 

 gradual way to 80° F. upon September 6. This was followed by a 

 gradual drop to 54° F. upon September 12. This rearing gave its 

 maximum daily migration when 39 days old and its 50 per cent of 

 migration four days later. 



The larvae considered in Part III of Table XXIV were a late rearing. 

 They had favorable weather to near the end of the second instar, 

 but very unfavorable weather during the twigward migration. The 



