as 
1914] Life History of Hydromyza Confluens. fod 
reach the surface and since this is true there would be no 
opportunity for the female to deposit the eggs, hence the 
constant freedom from infestation. Furthermore, in the region 
of Douglas Lake, the flowers do not reach the surface of the 
water until in late July and in August, a date which is much 
later than the time of oviposition, and as a consequence they are 
exempt from the attacks of the insect. 
The gall first becomes perceptible on the petiole as a slight, 
ovoid enlargement and can be detected by pulling the petiole 
between the fingers. Each gall is produced by one larva only 
and in no case is more than one larva found in a single gall. 
It is very probable that in the early stages the presence of the 
larva is not perceptible since this enlargement really occurs 
at a time when the larva is well toward maturity. As the 
time of pupation approaches the gall begins to turn brown, 
ultimately assuming a deep brown color, thus making it easy to 
detect. The shape of the exterior of the mature gall varies 
somewhat, usually appearing as an ovoid swelling, although 
it should be noted here that many of the galls do not increase 
the diameter of the petiole. The galls also vary in size to 
some extent, the length of those containing pupe ranging 
from 6 to 9 mm. They are always longer than broad, the 
long dimension being in the direction of the long axis of the 
petiole. 
The number of galls per petiole varies rather widely. Some- 
times only one gall occurs on a petiole, but usually the number 
is greater. In a large series of observations the maximum 
number on a single petiole was found to be 14 and many of 
the petioles contained as high as 13. In one of the series of 
counts in which 45 infested petioles were examined, 7 was 
found to be the average number of galls per petiole. No 
relation was found to exist between the length of the petiole 
and the number of galls. It might be assumed that the longer 
petioles contain the larger number of galls, but this was not 
always true. Numerous instances were observed in which a 
petiole, six feet in length contained only two or three galls, 
while a neighboring petiole, three feet in length, contained 
Los 12. 
Galls occur irregularly along the petiole and may be situated 
near the bottom, even in those almost six feet long. They may 
be distributed along the entire length of the petiole and well 
