328 EDWARD F. ADOLPH 
It is of interest to know whether flies will respond readily to 
single stimuli rather than to definite complexes of the environ- 
ment. The problem, as presented by Drosophila, was suggested 
by Dr. G. H. Parker, who constantly guided the course of the 
work and aided in its details. The experiments were carried on 
during the year 1915-16 in the ZoGdlogical Laboratory of Harvard 
College. 
EXPERIMENTS 
Drosophila melanogaster Meigen, commonly known as the 
little fruit fly or pomace fly, has been used extensively in experi- 
mental work. ‘The flies used in the present experiments - were 
from a heterogeneous laboratory stock to which wild and stray 
individuals had access. They breed readily in culture bottles 
containing banana fermented with yeast, while in the field they 
lay their eggs upon a variety of overripe fruits unprotected by 
skins (Lutz, 714), and on decomposing garbage (Evans, 16). 
The only conclusion which can be drawn from the literature is 
that the fruit flies oviposit on fruit and vegetable material which 
is undergoing acid fermentation. 
It has been commonly observed that flies which do not find 
their regular and accustomed conditions for egg-laying shed a 
few eggs at random. There are essentially two sets of factors 
in the process of oviposition: 1) the environmental set, which 
will release the ovipositing mechanism, and, 2) the previous 
formation and growth of the eggs. Obviously, the external 
factors cannot call forth a response until the internal processes 
have gone to completion. 
A. External factors 
Experiments were carried out by exposing female flies to var- 
ious simple conditions of environment, allowing them a day or 
two in which to deposit eggs, and then counting the number of 
eggs laid. Drosophila begins to lay its eggs about twenty-four 
hours after emergence from the pupa, and in general the produc- 
tivity does not depend upon the fertility, although the unfertil- 
ized eggs do not develop. The eggs are elongate and white, 
