MOTIONS OF INSECTS. 285 
must be furnished with means of locomotion proper to 
that element. To this class belongs the common gnat 
(Culex pipiens, L.), which being one of our greatest tor- 
ments, compels us to feel some curiosity about its history. 
Its larva is a very singular creature, furnished with a 
remarkable anal apparatus for respiration, by which it 
usually remains suspended ‘at the surface of the water. 
If disposed to descend, it seems to sink by the weight of 
its body; but when it would move upwards again, it ef 
fects its purpose by alternate contortions of the upper 
and lower halves of it, and thus it moves with much ce- 
lerity. The laminge or swimmers, which terminate its 
anus*, are doubtless of use to it in promoting this pur- 
pose. It does not, that I ever observed, move in a la- 
teral direction, but only from the surface downwards, 
and vice versa.—Another dipterous larva (Corethra culi- 
ciformis, Meig.) which much resembles that of the gnat 
in form, differs from it in its motions and station of re- 
pose. For, instead of being suspended at the surface 
with its head downwards, it usually, like fishes, remains 
in a horizontal position in the middle of the water. 
When it ascends to the surface, it is always by means of 
a few strokes of its tail, so that its motion is not equable, 
sed per saltus. It descends again gradually by its own 
weight, and regains its equilibrium by a single stroke of 
the tail®,—A well known fly (Stratyomis Chameleon, ¥.), 
in its first state an aquatic animal, often remains sus- 
pended, by its radiated anus, at the surface of the water, 
with its head downwards. But when it is disposed to 
seek the bottom or to descend, by bending the radii of 
@ Reaum. iv, ¢. 48. f. 3. nn. > De Geer, vi. 375. ¢, xxii. fi 4, 5. 
