EGG-LAYING REACTIONS IN POMACE FLY Sank 
those reared on a completely adequate medium such as yeast. 
He considers this reduction to depend upon the amount and 
quality of food. 
5. Periodicities. Back and Pemberton (14) find that the 
melon fly, at intervals of about a week, lays numerous eggs in 
one day. In Drosophila no observations were made upon indi- 
vidual flies throughout a lifetime. ‘There is a distinct tendency, 
however, for an individual fly to lay several eggs within a few 
minutes. How often such spasms occur under uniformly stimu- 
lating conditions is unknown, but there is certainly no daily or 
weekly periodicity among different individuals. 
6. Gregariousness. No difference was found in the responses 
of flies confined singly or in groups of varying numbers. ‘The 
presence of male flies had no effect. 
7. Inbreeding. Castle and his co-workers (’06) and Moenk- 
haus (11) show conclusively that no measurable change in the 
productivity is caused by the continuous mating of offspring of 
the same parents for many generations. Indeed, the inbreeding 
standardizes the wide divergence in productivity between differ- 
ent races taken in nature according to the latter author. 
8. Anesthesia. In the majority of experiments the flies were 
etherized before being placed under the experimental conditions. 
Occasionally a single egg was extruded during the excessive ac- 
tivity just preceding the anesthesia. Sturtevant (’15) notes that 
such an extrusion often occurs at death. Many experiments 
were performed in which the flies were not etherized or handled 
in any way. No difference in the responses then could be noted. 
Summary. The production of eggs within the body of the 
female fly therefore depends upon such factors as nutrition and 
vivacity, while their extrusion may be favored by such events as 
copulation and spasmodic activity of the ovipositing organs. 
DISCUSSION 
The egg-laying response in Drosophila may be considered 
diagrammatically as being caused by a succession of stimuli. 
The prerequisites are adeqate nutrition and sexual maturity, at 
least. The eggs, having been produced within the body of the 
