386 KATHARINE FOOT. 



METHODS AND RESULTS. 



In order to determine the sex of as large a number of the 

 offspring as possible I adopted a different method from that of 

 other investigators. Instead of waiting for the nymphs to 

 mature in order to determine the sex, they were dissected at any 

 stage that was convenient and those that died were not dis- 

 carded but dissected at once and the sex recorded. It was thus 

 possible to determine the sex of nearly all that were hatched. 



Our method of treating these insects makes it possible to col- 

 lect and isolate the eggs deposited each day, thus keeping an 

 accurate count of the number of eggs deposited daily and the 

 number hatched. 



Both the male and the female had the third moult in the 

 laboratory, the female July 22, 1919, and the male July 24. 



The male died August 26; he lived therefore 33 days after 

 maturity, thus exceeding the average length of life of P. vesli- 

 menti males. The female died September 5. She lived there- 

 fore 45 days after maturity, eleven days longer than the average 

 length of life of the females. She continued to deposit eggs 

 daily after the death of the male. She deposited in all 143 eggs 

 (116 before the death of the male and 27 after that date). She 

 commenced to lay eggs the 4th day after maturity and stopped 

 laying 2 days before she died. She deposited 2, 3, 4 or 5 eggs 

 each day. Of the 116 eggs laid before the male died, n failed 

 to hatch, but nearly all developed and three of the nymphs partly 

 emerged. Of the 27 eggs laid after the male died, seven failed 

 to hatch, but all were fertilized and four of the nymphs partly 

 emerged. 



The nymphs were raised in lots of 20, and the death rate was 

 relatively low in lots 1,2,3 an d 4- The death rate in lots 5 and 6 

 was much higher. Several of the nymphs died even before the 

 first moult. In some of these cases the nymphs were too dry to 

 dissect, and therefore the sex was undetermined. This higher 

 death rate was probably due to the age of the female, as the 

 death rate was progressively high towards the end of the experi- 

 ment. 



125 eggs were hatched and the sex was determined for 115 

 (62 males and 53 females). 42 died during the experiment and 



