1914] Life History of Hydromyza Confluens. 143 
which has been subjected to side to side strains such, as are pro- 
duced by wave action, and the window has thus been broken 
open. 
According to the observations of the writer, pupation 
occurs shortly after the window is completed and the pupa 
lies with the cephalic end in close proximity to the window. 
-In some cases the pupa lay so close to the window that the move- 
ments of the adult in escaping from the puparium would have 
been sufficient to open it. 
One of the characteristics of Nymphaea americana is the 
shape of the petiole. It is conspicuously flattened so that 
approximately one-third of the circumference is quite flat 
while the remaining two-thirds are very convex. For con- 
venience in discussion these surfaces will be designated as the 
plane surface and the convex surface. On the former there is a 
median, longitudinal ridge. Needham’s paper indicates nothing 
as to constancy or variation in the position of the window 
with reference to the two above-mentioned surfaces although he 
figures a gall with the window on the convex surface. The 
position of this window is variable, sometimes occurring on 
the plane surface and sometimes on the convex, but not in 
equal numbers and the writer was lead to make some observa- 
tions on this point. Of 226 galls examined at random the 
window in 137 occurred on the convex side and in the remaining 
51 cases on the plane surface. Various other counts not 
recorded in the above numbers showed similar results. Available 
data does not seem to offer an explanation for the predominance 
of the windows on the convex surface. 
THE ADULT. 
Broods.—Although the writer has no positive evidence as 
to the number of broods per summer, there seems to be the 
possibility of at least two. A few adults were observed about 
the Nymphaea beds during the first part of July, at least three 
weeks before the larve in the petioles were grown. The 
maximum appearance of the adults in 1913 occurred between 
August Ist and 6th. During the period, July 10-25, adults 
were very rare and it may be that this represents the interval 
between two successive appearances of the adults. Very 
few of these insects remained in the pupal stage after August 
