34 MASS. EXPERIMENT STATION BULLETIN 157. 



rupture the epidermis of the leaf and start a mine, and, when exposed on 

 the surface of the leaf by being taken out of the mine, or by rupturing the 

 epidermis which shields it, soon perishes. 



Qpiposition in Artificial Light. 

 .While engaged in making an observation one evening on some adult? 

 confined upon a leaf within a cheesecloth bag on a plant in the laboratory, 

 the writer noticed a female in the act of piercing the epidermis of the leaf. 

 Whether this was done for the purpose of merely feeding, or for ovipositing, 

 he was unable to say. To determine whether fertilized females would 

 oviposit in artificial light, two fertilized females were isolated in the 

 evening on a leaf within a cheesecloth bag on a plant placed in a darkened 

 room. The leaf on which these females were confined was exposed to a 

 fairly strong light, being about 15 inches from a 32 candle-power Mazda 

 lamp. At this distance the leaf seemed to be — as perceived by the palm 

 of the hand — just out of the higher temperature zone formed by the 

 radiation of the lamp. Also, the leaf was so placed as to receive a uniform 

 amount of hght on its two surfaces. 



The flies were removed from the leaf early next morning, having been 

 on it for a period of ten hours. On examination it was found that ovi- 

 position had taken place. Twenty-four larvse were subsequentlj^ counted. 



Oviposition in Absence of Light or Total Darkness. 



In this case five females that were caught at large on plants in the 

 insectary in the forenoon (four of these were taken as they disengaged 

 from mating) were isolated in the evening on a leaf within a cheesecloth bag 

 on a plant placed in a dark room. In addition, the portion of the plant 

 bearing that leaf was covered with a black cloth bag impervious to light. 

 The flies were removed early next morning, after being on the leaf for 

 nearly eleven hours. On examination, eggs were found to have been 

 deposited. Eight larvse hatched. 



Assuming that the number of larvae hatched in this experiment, as well 

 as in the preceding one, represents the number of eggs laid in each, it is at 

 once apparent that the number of eggs laid per female by the five females 

 in absence of light was much smaller than the number laid per female by 

 the two females in artificial light, the proportion being 1.6:12. Also, it 

 should be borne in mind, that as the five females were taken in the morning 

 and were not placed on the leaf until evening, they had neither the oppor- 

 tunity to feed nor to oviposit for a period of about ten hours previous to 

 being placed on the leaf. These facts, in conjunction with their usual 

 inactivity in darkness under normal conditions, leads the writer to beheve 

 that under normal and natural conditions oviposition in absence of Ught 

 does not take place, and that the few eggs laid by the females in the ex- 

 periment were due in all probabiUty to the abnormal conditions to which 

 these females were subjected previous to their isolation on the leaf. 



Again, it is possible that some of the eggs were deposited while the flies 



