the water.
In some of these, as in the Cod and Haddock, a red membrane, consisting
of a great number of leaves or duplicatures, is found within the air-bag,
which probably secretes this air from the blood of the animal. (Monro.
Physiol. of Fish. p. 28.) To determine whether this air, when first
separated from the blood of the animal or plant, be dephlogisticated air,
is worthy inquiry. The bladder-sena (Colutea), and bladder-nut
(Staphylaea), have their seed-vessels distended with air; the Ketmia has
the upper joint of the stem immediately under the receptacle of the flower
much distended with air; these seem to be analogous to the air-vessel at
the broad end of the egg, and may probably become less pure as the seed
ripens: some, which I tried, had the purity of the surrounding atmosphere.
The air at the broad end of the egg is probably an organ serving the
purpose of respiration to the young chick, some of whose vessels are
spread upon it like a placenta, or permeate it. Many are of opinion that
even the placenta of the human fetus, and cotyledons of quadrupeds, are
respiratory organs rather than nutritious ones.

The air in the hollow stems of grasses, and of some umbelliferous plants,
bears analogy to the air in the quills, and in some of the bones of
birds; supplying the place of the pith, which shrivels up after it has
performed its office of protruding the young stem or feather. Some of
these cavities of the bones are said to communicate with the lungs in
birds. Phil. Trans.

The air-bladders of fish are nicely adapted to their intended purpose;
for though they render them buoyant near the surface without the labour
of using their fins, yet, when they rest at greater depths, they are no
inconvenience, as the increased pressure of the water condenses the air
which they contain into less space. Thus, if a cork or bladder of air was
immersed a very great depth in the ocean, it would be so much compressed,
as to become specifically as heavy as the water, and would remain there.
It is probable the unfortunate Mr. Day, who was drowned in a diving-ship
of his own construction, miscarried from not attending to this
circumstance: it is probable the quantity of air he took down with him,
if he descended much lower than he expected, was condensed into so small
a space as not to render the ship buoyant when he endeavoured to ascend.]

Her _secret_ vows the Cyprian Queen approves,
410 And hovering halcyons guard h