36 MASS. EXPERIMENT STATION BULLETIN 157. 



Number of Eggs laid by a Female. 



The above experiments for the determination of the length of the egg- 

 laying period were used also as a means for ascertaining the number of eggs 

 laid by a female during her lifetime. 



As the marguerite leaves on which the flies were confined were not very 

 large, and as a large number of eggs was laid during some of the periods 

 during which each female was kept on a single leaf, it was not possible 

 to count with any degree of accuracy the number of eggs laid during that 

 period. Instead of the eggs, therefore, the larvae were counted. The 

 newly hatched larva, just as soon as it was recorded, was kiUed by being 

 stabbed with a needle. It was thus prevented from obscuring and masking 

 other larvae by its mining. In this way, also, the possibility of its being 

 counted more than once was obviated. But even with these precautions 

 — owing to their escaping death — quite a number had to be denominated 

 as doubtful. 



The female, in March, wliich oviposited for sixteen days out of twenty- 

 one which constituted her adult life, produced 141 larvae. If 28 are sub- 

 tracted from this number as having possibly been counted twice, she 

 produced only 113. As this female was shifted from leaf to leaf daily, 

 there is a record of the number of eggs laid every day during the entire 

 period. The distribution was as follows: — 



21219351 2 2 ^^ • 



1-10-3-12-8-16-6-14-11-6-8-7-4-4-2-1 113 



The upper series of figures represents the doubtful ones. 



From this record it is seen that on the first day of the egg-laying period 

 only one egg was deposited, and that similarly only one was laid on the 

 last day; that the greatest number for a single day was deposited the 

 sixth day; that there was in a general way a gradual decrease from the 

 eleventh day to the last; that about two- thirds of the entire number 

 were deposited during the first half of the period. Another interesting 

 feature is seen in the alternation in the relative number of eggs laid, or 

 the rise and fall of the numbers laid, from day to day, during the first half 

 of the period. 



The female, in March and April, which oviposited for eighteen days out 

 of the twenty-one which constituted her adult life, produced 136 larvae, 

 but 16 must be counted as doubtful. This number, however, does not 

 represent the total number, as the leaves on which the female was kept 

 from the twelfth day to the seventeenth, inclusive, were accidentally 

 detached from the plant and were lost as far as results were concerned. 

 A daily record is not available in this case. 



The female, during the latter part of May, which oviposited for fifteen 

 days out of the seventeen which constituted her adult life, produced 25 

 larvae, 5 of which are doubtful, and deposited 76 eggs, larvae and eggs 



