2. (Zo["o]l.)
(a) One of the tubes or folds of the mantle border of a
bivalve or gastropod mollusk by which water is
conducted into the gill cavity. See Illust. under
{Mya}, and {Lamellibranchiata}.
(b) The anterior prolongation of the margin of any
gastropod shell for the protection of the soft siphon.
(c) The tubular organ through which water is ejected from
the gill cavity of a cephaloid. It serves as a
locomotive organ, by guiding and confining the jet of
water. Called also {siphuncle}. See Illust. under
{Loligo}, and {Dibranchiata}.
(d) The siphuncle of a cephalopod shell.
(e) The sucking proboscis of certain parasitic insects and
crustaceans.
(f) A sproutlike prolongation in front of the mouth of
many gephyreans.
(g) A tubular organ connected both with the esophagus and
the intestine of certain sea urchins and annelids.
{Inverted siphon}, a tube bent like a siphon, but having the
branches turned upward; specifically (Hydraulic
Engineering), a pipe for conducting water beneath a
depressed place, as from one hill to another across an
intervening valley, following the depression of the
ground.
{Siphon barometer}. See under {Barometer}.
{Siphon bottle}, a bottle for holding a["e]rated water, which
is driven out through a bent tube in the neck by the gas
within the bottle when a valve in the tube is opened; --
called also {gazogene}, and {siphoid}.