IIYDKADKPHAGA. 
81 
p. 17) is, when full-grown, about two inches long, 
dirty brown in colour, and tapering to the tail, which 
is provided with two thin appendages fringed with 
hairs. The larva suspends itself in the water, head 
upwards, with these appendages at the surface, and 
thus obtains air; for the ordinary breathing-holes on 
the sides are closed up, and the air-vessels are reached 
by means of two spiracles at the apex of the eleventh 
segment near the fringed extremity. Its head is 
large and oval, with composite eyes (Fig. 1 a, p. 17), 
rudimentary antennas, and very long, sickle-shaped, 
pointed jaws, which are channelled so as to allow the 
larva to extract the juices of its prey, there being no 
opening at the mouth. It is very rapacious, and is 
often called the “ Fresh-water Shrimp.” 
Cybister, reputed British, has its wing-cases widened 
behind, and not furrowed in the female. Acilius 
sulcatus, a moderately large, common, flat, grey species, 
has been observed to make a considerable humming 
noise, apparently produced by the action of the air 
upon the alulce or winglets, two small circular mem- 
branous plates at the base of the elytra (Fig. 8 li, 
p. 33). 
The GYRINIDyE differ vastly in structure from all 
the above. They have four eyes ; two on each side, one 
above and one below (Plate III., Fig. 6 a ) ; the ordi- 
nary single eye being divided by the cup formed for 
the articulation of the antennae : the palpiform outer 
lobe of their maxillae is wanting, except in the genus 
Gyrinus, where it is extremely small, slender, and 
rudimentary; their antennae are short, robust, and 
stiff, the second joint being very large and ear-like, 
with the third and remaining joints jammed together 
a 
