DIPTEROUS LEAF-GALLS ON OAK. 207 
well-developed gall two larvae, the two cells sometimes separated, but more gener- 
ally running into one. The larva is of the usual orange color, but appears to be 
somewhat shorter and thicker than those I have before noticed. Length, when not 
crawling, .14 of an inch. Head quite pointed, and the first few segments doubly 
wrinkled. Two appendages at head, and two brown spots near it superiorly. Breast- 
bone brown and clove-shaped. Terminal segment with two acute prominences. 
October 29, 1869. Upon opening several galls to-day, I found one which contained 
four larvae, two in each cell. 
January 1, 1870. Many of the larvae are on top of the ground, though most of them 
are yet in the galls. Some of the galls have become softer, and have peeled open ; 
and it is from these, I think, that the larvae have escaped. 
April 3. I examined them to-day and find that, though some of them are empty, the 
great majority of them contain either pupae or larvae. The larva works and loosens 
a passage, pushing the de'bris to the surface. It then lines its cell with a delicate 
silken lining, and transforms to a pupa of the exact color of the larva ; the head being 
furnished behind the antenna? with two thorns ; the wing-sheaths reaching to the 
third abdominal joint, and the hind legs, which are free from the body, to the fifth. 
Many of the galls contain a white parasitic maggot with a conspicuous black pointed 
head, divided longitudinally with a lighter line and with two brown spots behind it. 
May 2, 1870. Many of the flies have issued, but all so far seem to be females. The 
antennae are 14-jointed (double jointed -f- 12) and are scarcely at all verticillate, and 
only the slightest restriction on basal one; no pedicels; length of joints very grad- 
ually decreasing from 3 to 14. Nervules of wings as in true Cecidomyia. On opening 
many galls to-day I find most of the larvae within cells. A great number of parasites 
have issued within the past few days, and on opening the galls I find the perfect para- 
site within a cell between two others occupied by Cecidomyia larvae. So many of 
the galls are empty, that I greatly incline to believe some of the larvae left them 
and entered the ground, the more so that the pupal integuments were all on the 
ground. 
July 22, 1870. Larva just hatched and barely visible. Gall itself fully formed and 
golden yellow. (MSS. notes. Also see Amer. Ent., Vol. II, p. 29.) 
289. Cecidomyia quercus-majalis Osten Sacken. 
Blister-like gall of Cecidomyia on young leaves of the pin-oak 
( Quercus jtalastris). Generally these galls occur on the principal ribs 
of the leaf; sometimes between the ribs. They are oblong, blister-like, 
the hollow surface somewhat uneven, wrinkled, walls thin ; color pale 
green or reddish. They bulge out on one side of the leaf and have a 
longitudinal slit on the other. Galls projecting on the under side of 
the leaf and having the slit on the upper side seem to be somewhat 
more common than those of the opposite description. The slit can be 
opened without injuring the gall by gently pulling at the sides. Such 
galls which grow upou a rib show a trace of it on their longitudinal 
diameter. The larva, which can be taken out of the slit without lacer- 
ating the gall, is rather larger than the majority of the larvae of Ceci- 
domyia (about 0.2 of an inch long), and not reddish, as usual, but white, 
smooth ; the breast-bone is hardly visible, as its front part only is horny, 
having the appearance of a transverse, reddish-brown wavy line." The 
last abdominal segment has several minute, fleshy, pointed projections. 
The larva drops to the ground through the slit at a certain period of its 
development; hence, empty galls are often found. Found in consid- 
