MONOCULUS. 497 
or a claw broken off on each side at the second 
joint or elbow; on these extremities are the eyes, 
like those of the horns of snails, but under the 
covert of a thick and opake shell Nature in that 
place has wonderfully contrived a transparent 
lantern, through which the light is conveyed, 
whose superficies very exactly resembles tlie great 
eyes of our large libellae or adderbolts, which to 
the naked eye are plainly perceived to be com- 
posed of innumerable globuli: these, like them, 
are oblong, and guarded by a testaceous super- 
cilium.” 
Of the European Monoculi by far the largest is 
the Monociilus ApuSy which, when full-grown, mea- 
sures nearly an inch and three quarters from the 
front to the end of the body, exclusive of the 
forked divisions of the tail. It is found in muddy 
stagnant waters, but is a rare species in this 
country, having been only observed in a few par- 
ticular situations. In its general shape it is con- 
siderably allied to the large exotic species before 
described, but the body is of a more lengthened 
form in proportion, with the hinder part naked, 
and divided into numerous joints: the branchim 
or respiratory organs, are large, and are distri- 
buted into numerous imbricated rows on the under 
part of the body: beneath the front is a pair of 
jointed, trifid arms, extending on each side to a 
considerable distance: the eyes are placed near 
each other in front of the shell: the tail is termin- 
ated by a pair of long forks or setaceous processes. 
The colour of tlie whole insect is a pale greenish 
32 
V. VI. P. II. 
