228 THE ESSEX NATURALIST.
the surface-film, the flaps open, forming a sort of cup into which
the water does not penetrate, and the surface-film clinging to
the edges of the cup is drawn down into a capillary depression,
which exerts the upward pull necessary to keep the larva, though
heavier than water, suspended from the surface. That the
water does not penetrate into the cup must be due to the water-
repellent nature of at least its inner surface and the edges of
the flaps. Whether the outsides of the flaps are water-repellent
or not has not been ascertained. Owing to the position of the
siphon at the hinder end of the body, the larva hangs head down-
wards and therefore it does not feed directly on substances
floating on the surface, but on such small plants and animals
and other organic particles as happen to be a little below the
surface.
In Anopheles the larva still has the ends of its respiratory
vessel opening on the eighth abdominal segment, but there is
no siphon. On the other hand each of five of the abdominal
segments is furnished dorsally with a pair of very peculiar stellate
hairs, alluded to as float-hairs, looking not unlike miniature
shuttlecocks. When the larva comes to the surface it brings its
whole back into contact with the surface-film and it appears that
the float-hairs penetrate the surface-film and produce capillary
depressions which, together with that produced by the respiratory
opening, are of sufficient size to maintain the animal in a hori-
zontal position at the surface, although it is slightly heavier
than water. Suspended in this way the larva proceeds to feed
and it does this by turning its head completely round, so as to
face upwards, and sweeping into its mouth any suitable organic
matter it can find on the surface-film.
The larvae of some other Dipterous insects such as Stratiomys
chamaeleon and the larvae of a few beetles such as Hydrobius
fuscipes suspend themselves by their tails from the surface-
film by much the same method as the Culicine larvae, namely,
by a sort of cup which remains dry, at least on the inner side
and edges. In the first-named the cup is a very beautiful
structure formed by some thirty barbed filaments set in a ring
at the tip of the tail. These meet together at their extremities
when under water, enclosing a bubble of air, but open out to
form a conical cup upon striking the surface-film.
Of the Entomostraca systematically using the surface-film