April, '09] 



JOURNAL OF ECONOMIC ENTOMOLOGY 



185 



are doubtless accounted for by embryonic development being entirely 

 suspended during cool "weather, and it is not impossible that the via- 

 bility of eggs may be entirely destroyed by a temperature as low as 

 25 or 30°, but on this point we are as yet undecided. 



The period of incubation has been determined, ordinarily, by plac- 

 ing a queen and workers, but no immature stages, in an artificial for- 

 micary and then noting the time from deposition of the first egg to 

 appearance of the first larva. This period was assumed to be the 

 real period required for incubation. In other cases, single groups, 

 of eggs have been kept under constant observation throughout the 

 entire period of incubation. The following table shows the varia- 

 tion in development at different seasons, together with the average 

 daily mean temperatures prevailing: 



TABLE I 

 Ddbation op Egg Stage at Different Seasons— Wohkeb 



The Larva 



The larva when first hatched is not distingTiishable from the egg 

 without the assistance of a magnifying glass. For a time after hatch- 

 ing the body is severely curved, the cephalic end being almost in 

 touch with the caudal end, but as development progresses the larva 

 assumes more and more of a straight form. The curvature is not 

 entirely lost, however. A recently hatched larva, measured with the 

 compound microscope and eye-piece micrometer, measured .49 mm. 

 long by .32 wide. The fully grown larvae (workers) average 1.7 mm! 

 long by .66 mm. wide. The largest one under our observation meas- 

 ured 1.87 mm. by .765 mm. 



*Cages kept in office ; record of exact temperatures not available. The bal- 

 ance of the records were made in the "formicarium" and the recording instru- 

 ments kept in the same room with the cages, hence the temperature and 

 humidity records are correct for the exact location of the eggs under observa- 

 tion. 



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