Dec, 1907.] GiRAULT : BIOLOGICAL NOTES ON MeGILLA. 



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or never exposed to the direct rays of the sun, being under a leaf, but it 

 is a question whether the conditions of their usual environment are 

 obtained in the laboratory. 



Period of Incubation. 



Table I. 

 Period of Incubation, May 24- June id, 1907. 



Duration of Posfembryouic Instars. 



In Table II the duration of the different stages after hatching are 

 shown for a single generation, from May 25 to June 23. The larvae 

 were fed on various aphids which were supplied them in abundance, 

 and they were confined separately under the conditions stated in regard 

 to the eggs, as were also the pupae. 



The sums of effective temperature for the different individuals of 

 this generation vary for over seventy degrees, when it appears that 

 they should be very nearly alike, other conditions being equal. It 

 would seem as if equal amounts of effective temperature should cause 

 equal amounts of growth or development in individuals of the same 

 age, providing food and other factors of environment are equal, but 

 apparently there are also internal factors involved, causing certain in- 

 dividuals to deviate in either direction from the average. The indi- 

 vidual instars vary considerably from a little less than two days to a 

 little more than nine days, but this larger variation in the duration of 

 separate instars or stages does not affect the length of the entire life- 

 cycle, one stage generally making up what the other loses. 



Adults in Confinement. 

 A pair of mating adults captured on the foliage of blackberry at 

 II A. M., May 24 and confined, produced but 17 eggs, the female 

 dying on June 8. These eggs were deposited on May 24 (5) and 



