144 
Prof. Miall and Mr. N. Walker on the 
a dorsal projection of the eighth segment, which over- 
hangs the anus. Each filament is set with very fine hairs, 
so that it somewhat resembles a plume.* 
The larva may often be seen to run the anal filaments 
through its mouthy thus cleansing them from diatoms, 
desmids, etc., which are probably devoured. 
The head is rather small, and completely exserted. On 
its upper surface the triangular clypeus, pointed behind, 
occupies a central position ; it is flanked by the two 
epicranial plates ; all are ornamented with a symmetrical 
pattern of numerous tubercles. The minute antenna 
ends in several short rods of equal size and similar shape. 
On the sides of the head behind the antennae are the 
eye-spots, which are oval, convex, and pigmented. The 
labrum is prominent, setose, and very movable, being 
continually flexed and extended by the living larva. On 
either side of the labrum, and closely applied to it, is a 
jointed setose appendage. The mandibles are strong, 
bent at an elbow, and palmate, each with five pointed 
teeth ; there is a bunch of setae on the elbow, and also a 
row of setEe on the inner side. When closed, the mandi- 
bles do not interlock, but are rotated so far backwards 
that their bases are in front and the teeth behind, the 
elbow then appearing upon or near the margin of the 
head. Two lobes, each bearing two bunches of seta3 and 
stiflfened by several chitinous plates, appear to represent 
the maxilhe. The submentum is a transverse comb-like 
plate with about twenty denticles, which increase in size 
outwards, the most external being three times the size of 
the next. In front of this comb are the openings of the 
salivary ducts and a hairy patch, which is the free end of 
the labium. All the mouth parts are enclosed in a sunk 
and roughly hexagonal space, which occupies the fore 
part of the ventral surface of the head. The margin of 
this space is stiffened by a special rim. 
The larv« seem most at home in water just deep 
enough to cover the body. They then bury themselves 
in mud, sand, or algse, bringing the tip of the abdomen 
to the surface of the water. The outspread fringes of 
the four processes then form a cup, filled with air, and 
from this air can be taken into the spiracle. A larva 
The larvjE of Pa;clIostola (Brauer, Zweifl. d. Kais Museums, 
iii., fig. 11) has two pairs of siinilarly placed processes, shortly 
fringed at the extremities only. 
