155 
Larvae of a Dipterous Insect. 
are nearly equal. Third similar to the second, but its greatest 
breadth nearly double its length. Fourth and succeeding segments 
also similar, but with their lateral margins more rounded, and their 
transverse diameters continually increasing to the seventh, then 
again diminishing. Eleventh, or terminal segment, viewed dor- 
sally, of a somewhat semicircular form, its posterior margin being 
curved in a very regular manner. But on the ventral surface of 
the abdomen this segment is much less developed, and of a differ- 
ent form, being similar to the one preceding it, only smaller ; 
behind it, also, is the anus, the lips of which appear to arise from 
the doubling of another rudimentary segment, representing the 
twelfth, and thus making up the typical number. 
The first two segments of the body are much depressed, and 
bounded at the sides by a sharp edge common to both their dor- 
sal and ventral surfaces. The remaining segments, which are 
thicker and more elevated, have the lateral margins of their two 
surfaces separated by an intermediate space of a softer texture, 
occupying the sides of the abdomen. 
All the segments, excepting the first, are furnished with 
appendages apparently analogous to branchiae. In the second 
segment there is but one of these appendages on each side, but 
in that of the third, and succeeding ones to the tenth, there are 
two, the upper one being attached to the dorsal, the lower one to 
the ventral, surface of the segment. The eleventh, or terminal 
segment, is set with six of these appendages, all arising however 
from the dorsal surface, and arranged semicircularly in one plane 
round the extremity of the body. These pseudo-branchial ap- 
pendages become more developed, and more fringed with ramifi- 
cations, as they approach the posterior extremity ; the first pair, 
or those attached to the second segment, being nearly simple, or 
appearing as if clothed only with a fine pubescence. 
The above segments are also furnished dorsally each with a 
pair of minute soft processes fringed with bristles, which, when 
viewed in the aggregate, form a double longitudinal series down 
the back. On the eleventh, or terminal segment, their place is 
taken by two stouter, somewhat corneous papillae, of a cylindric 
form at bottom, but conical upwards, the apex being perforated 
with three orifices. These last are evidently air-tubes, which ap- 
pear to be connected by internal trachae with those on the sides of 
the head already spoken of. 
There is also a double longitudinal row of still more minute 
processes on the ventral portion of the body, a pair occupying 
each of the same segments above alluded to, but placed more la- 
