EGG-LAYING REACTIONS IN POMACE FLY 335 
substances were diluted many times, no concentration was found 
low enough to fail to call forth responses, very faint odors having 
full stimulating value. ‘Thus, flies laid eggs readily in contact 
with 0.0001 per cent formic acid solution and 0.0003 per cent 
ethyl alcohol. 
Light had no influence upon the response. Experiments with 
successful stimuli were carried out in the dark, in artificial elec- 
tric light, in diffuse daylight, and in direct sunlight. Sight 
plays no part in finding a suitable locality for the deposition of 
eggs. 
TABLE 3 
Summary of non-selective experiments 
= = AVERAGE NO. 
KIND OF STIMULUS SUBSTANCES MA eUNeS! CLRELLNS FORTH THE EGGS PER DAY 
LARGEST RESPONSE PER FLY 
INiaxs tama ulus fabeteatie 4 cveinys dkny tev a dry glass 0.05 
ONCOL A SEAS Sees ‘OS eae acetic acid + alcohol 0.06 
MONS TUE cs sere. a cGcosrsa iets: water 0.18 
SUSISUOS cease Ans ine Ieee ae ee glucose + water 0.20 
WMder-itastesers) ees baicia dees: ethyl ether 0.21 
“TRERSTHEURS Decree 9 Onc Bie eRe OTE Eee boiled agar 0.77 
MextURe = Od OF calc ccrecslen ae. boiled agar-+ ethyl] alcohol PRG 
Texture + taste + odor.......... fermenting banana 3.3 
No observations were made of the acidity and alkalinity of 
the media upon which the flies laid their eggs. According to 
Morgan (715), cultures of fermenting banana become alkaline 
after ten or twelve days when the flies are breeding upon them. 
He says ‘‘on alkaline food the flies usually refused to lay eggs.” 
The banana media used in the present experiments never became 
as old as this. Agar is well known to be uniformly alkaline, 
usually sufficiently so to give a pink color with phenolphthalein 
(Fellers, ’16), yet copious responses were obtained with this 
medium. 
The effect of temperature conditions was not studied, but its 
general influence is indicated below. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 31, NO. 3 
