PREOVIPOSITION PERIOD OF THE HOUSE FLY. 11 
Bishopp, Dove, and Parman are doubtless correct in saying that in 
general ‘‘increased humidity seems to hasten egg laying.’’ 
The present results agree also with the Dallas observations in 
showing that the food supply of the adult flies has an important 
influence on the length of the preoviposition period. Banana, water, 
and manure was found to be a favorable combination in these experi- 
ments. Lack of moisture always proved fatal to flies, and without 
food they die within two or three days. 
Yet temperature, humidity, and food supply are not the only 
factors which influence egg laying. If Table I be examined, such 
apparently contradictory results as an 8-day record at an average 
mean temperature of 72° F. (see No. 20) and a 12-day record at an 
average mean temperature of 76° F. (see No. 39) will be found. 
Mr. Pomeroy has suggested, and the writer is strongly of the opinion, 
that the kind and quality of the larval food is partly responsible for such 
apparent discrepancies. It is a well-known fact that the amount and 
kind of larval food have a marked influence on the size of the resulting 
adult flies, and there is no reason to doubt that the physiological 
activities of the adult are likewise affected. It appears in Table I 
that most of the shorter preoviposition records were obtained with 
flies which had been bred from larve fed on moist bran or a bran- 
manuremixture. From media which fermented less actively than these, 
or which were allowed to dry out, or were too small in quantity, the re- 
sulting flies were not only small but often failed to oviposit at all 
and usually lived a shorter time than large flies under the same con- 
ditions. Some larve bred exclusively on rotten potato produced a 
small race of flies which did not oviposit, due perhaps to the pre- 
ponderance of starch in their diet. Griffith (1908) observes that 
small flies are incapable of reproduction. 
In the experiments with isolated pairs of flies only 7 out of 30, or 
about 24 per cent, gave any positive results as regards the deposition 
of eggs. In the other experiments where a number of flies (8 to 200) 
were used in each lot, 70 out of 110, or about 63 per cent, gave positive 
results. It is possible that this may be accounted for by what may 
be called a psychological factor. The habit of the adult females of 
associating in large numbers in one favored spot in depositing eggs has 
been previously pointed out (Bishopp, Dove, and Parman, 1915), and 
it is probable that the isolation of a pair of flies is an abnormal con- 
dition which has its inhibiting effect. 
As regards the number of depositions, the Arlington observations 
again agree with those made at Dallas in that it was impossible to 
obtain more than two lots of eggs from a single female, but this does 
not prove, of course, that under normal conditions the adult fly can 
not oviposit oftener. Griffith (1908) gives no details of experiments 
