1914] Life History of Hydromyza Confluens. 139 © 
behind others in development, the differences did not seem to 
be sufficiently marked to warrant the conclusion that the 
eggs were deposited at different times, and (2) in some cases 
those lagging behind occurred in the middle of the petiole, 
while those towards the upper and lower extremities of the 
petiole developed at the same time, a condition which would 
not be likely to happen in case the eggs were laid by different 
females. The above evidence is not entirely conclusive but 
it seems to support the more feasible explanation, namely, 
that the eggs on a petiole are all laid at one time, and that the 
variation in the degree of development is possibly due to 
internal or external factors, probably the former since the 
external conditions seem perfectly uniform for all those deposited 
on a given petiole. 
Activity—Like many other dipterous larve, this gall 
maker is very sluggish. Specimens, removed from galls, 
showed only slow, squirming movements which were very 
ineffective so far as locomotion was concerned. The activities 
of these larve could be observed to some extent by holding an 
infested petiole between the eye and the source of light. The 
feeding activities appeared to be very deliberate. 
Effect on the food plant.—As mentioned above, the first 
evidence of infestation is the presence of a slight, ovoid swelling 
at. various places along the petiole. Later these swellings 
begin to develop-a brownish color, ultimately becoming a deep 
brown. About this time or a little later the entire petiole 
loses its green color, takes on a yellow appearance, and shortly 
afterwards the entire leaf begins to turn yellow, showing signs 
of deterioration. During the last week in July and the first 
week in August of 1913 one could readily pick out the infested 
lilies by the yellowish leaves. This work of the larve leads 
to the decay of both leaf and petiole. The nature of the 
injury is simple. The larve affect the plant in two different . 
ways: (1) The larva, as it eats out the internal cavity of the 
gall, severs the vessels which connect the leaf with the root- 
stalk, this alone being sufficient cause for the decay of the 
leaves. It was found that the heavily infested petioles deter- 
iorated no more rapidly than did the slightly infested ones 
and that one larva is just as efficient as several in causing the 
death of the leaf. (2) These galls produce weak spots in the 
petioles so that wave action breaks them at the points of 
