Vol.. 8, 1922 
BIOLOGY: PEARL AND PARKER 
213 
individual in a given volume of water (working with such organisms as 
infusoria, planarians, hydra, tadpoles, etc.), will be sub-lethal if several 
individuals are present in the same fixed volume of water. 
Without undertaking at this time any systematic review of the litera- 
ture on this subject it is our purpose in this paper to present some experi- 
mental data on the influence of density of population upon a different 
biological function than those mentioned above, namely specific repro- 
ductive rate. This variable we define as measured by the number of 
adults (imagoes) produced per mated female per day over a specified 
period. Our interest in this problem arose originally from purely practical 
considerations. Anyone doing experimental work with Drosophila has 
constantly arising this situation: he wishes to start an experiment with 
a large number of flies of homogeneous make-up as a group. What is the 
most expeditious way to get the desired numbers while still maintaining 
the requirement of homogeneity? Is it better to mate a considerable 
number of pairs in one bottle, to furnish the desired progeny, and if so, 
how many pairs ? Or is it better to mate up one or two pairs only in each 
of several bottles? W^hich plan will give the largest progeny group? 
Not being able to answer this practically important question satisfactorily 
either by a priori reasoning, or by perusal of the Drosophila literature, 
it was decided to test it experimentally. The results proved to have a 
considerably wider interest than that implied in the purely practical 
question. 
Plan of Experiment. — Mass matings were made on March 21, 1921 of 
flies from our line 107, the characteristics of which have been described 
by Pearl and Parker.^ When the offspring from the matings emerged 
they were used to make up the matings of this experiment, according to 
the following plan. Half pint milk bottles were used, and the food ar- 
rangements, etc., were according to the standard Drosophila technique of 
this laboratory, fully described by Pearl and Parker.^ The composition 
of the matings was as follows: 
SERIES NO. OP MATED PAIRS IN SERIES NO. OF MATED PAIRS IN 
BOTTIvES EACH BOTTLE AT BOTTLES EACH BOTTLE AT 
START START 
14 1 9 4 9 
2 4 2 10 3 10 
3 4 3 11 3 12 
4 4 4 12 3 15 
5 4 5 13 3 20 
6 4 6 14 1 25 
7 4 7 15 3 30 
8 4 8 16 2 50 
These bottles were put into a 25° incubator. At the end of 8 days the 
parent flies still surviving were transferred to fresh half pint bottles and 
allowed to continue breeding for a second period of 8 days. 
