470 



NEW YORK STATE MU8EUM 



head in the succeeding stages. The ratio was found to be 1.178. From 

 time to time larvre were taken from the cage, measured, and the results 

 tabulated. A definite increase in the width of the head was attributed 

 to molting. Considering that the larvae measured came from several 

 lots of eggs laid at different times, the figures given below are remark- 

 ably constant. Occasionally a larva would be found with a width of 

 head intermediate, but most of the time they were easily referred to 

 one stage or the other. In the earlier stages there was greater constancy, 

 as one might expect. 



Width of Head. 



STAGE. 



1 



2 

 3 

 4 

 5 

 6 

 7 



Measured. 



0.5625 

 0.6625 

 0.7750 

 0.9375 

 1.0625 

 1.3255 

 1.5000 



Calculated . 



0.7800 

 0.9194 

 1.0830 

 1.2760 

 1.4950 



Differences 



.0050 

 .0181 

 .021 5 

 .0495 

 .0050 



Proportion- 

 ate error.* 



.0066 

 ,0193 

 ,0183 

 ,0373 

 ,0033. 



If this ratio be constant, seven stages were recognized within two 

 weeks after the first larva was found. It was probably several days 

 old when found, and there may have been older larvae in the cage. 

 There could have been none more than six days old at the time, because 

 it takes six days for the eggs to hatch, and the insects had been in the 

 cage but twelve days. It is hardly likely that oviposition occurred 

 during the first few days. The seventh stage was reached within 

 twenty, and possibly, within sixteen days after the larva emerged from 

 the egg. In another cage, one reached the sixth stage within twelve 

 days after it emerged from the egg. That is, it molted six times in 

 seven or eight days. This result was obtained with larvae of known 

 age, and the time of the first molt was also known. The 

 seventh stage was attained by one larva August 14. Up till 

 August 22 the cige, from which this was taken, was under the closest 

 supervision, a constant watch being kept for a possible eighth stage. 

 August 22 a portion of this cage was thoroughly examined and some 

 twenty larvae removed; but none were larger than those taken earlier. 

 A close watch was kept on a smaller lot of larvae until September 11> 

 but no later stage was discovered. It would, therefore, appear that the 

 seventh stage might be the limit of growth. As the larvae reached 



* Obtained by dividing the difference by actual width. 



