336 EDWARD F. ADOLPH 
B. Internal factors 
Experiments with small numbers of flies were undertaken in 
order to see what prerequisites were necessary for response to 
appropriate environmental conditions. 
1. Age. Female flies begin laying eggs about forty-eight hours 
after emergence from the pupa (Lutz, ’14), the time of reaching 
sexual maturity depending upon the temperature. A large 
number of experiments were tried with flies of known ages up to 
twenty-one days. No response was given on the first day, but 
responses occurred on the second day of adult life, and uni- 
formly throughout the other days. Age therefore has no influ- 
ence after sexual maturity is reached. 
2. Fertility. Eggs are produced by flies which have not copu- 
lated, but, according to Guyénot (713, VI), these eggs do not 
develop. This author (13, VII) says that mating is a stimulus 
to egg-laying, with the result that eggs are laid so soon after 
copulation that they have not been fertilized. This is a clear 
case of stimulation. No data were obtained by me upon this 
point, except that two or three females known to be sterile laid 
no eggs in the first four days after emergence, which supports 
Guyénot’s statement that egg-laying is delayed three to thirteen 
days by failure to mate. 
3. General activity. Light is known to be an activating stimulus 
as well as a directive one in locomotor responses of Drosophila ~ 
(Carpenter, ’05). Casual observations indicate that odors and 
high temperatures are also such kinetic influences, and there 
may be many more. This energizing is sometimes of a gener- 
alized nature, so that all activities are increased by it. Thus 
Loeb and Northrop (16) find that the length of the life stages 
has a temperature coefficient comparable to kinetic activity in 
chemical reactions. No data are available as to whether the 
rate of egg-laying is proportional to the speed of other bodily 
movements. | 
4. Nutritive condition. Guyénot (718, IV, ’13, VI) states that 
females which have been reared upon a medium poor in nutri- 
ment, such as sterile potato, form considerably fewer eggs than 
