P. H. GOSSE, _del._ LEIGHTON, BROS.
FORBESIAN ÆQUOREA.
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The polypite is peculiar, and would scarcely be recognised as of the
same nature with the lively bottle-shaped organs of the Portuguese
man-of-war, or the long nimble tongue of the Sarsia. It forms a very
wide circle on the flat roof of the bell, whence the four large
triangular lips descend, which are cut into a minutely divided fringe
of filaments, that wave loosely in the water. There are about seventy
slender vessels which radiate from the polypite circle along the roof
to the margin, where they join the circular marginal vessel. I have
said that the tentacles are about thirty-six in all; that is, about
half as many as the radiating vessels, though the relation of number
is not exact. They hang down in the usual form, to the unassisted eye
appearing as excessively slender whitish or flesh-coloured threads,
capable of great elongation, or of contraction into ovate spiral
masses, hardly perceptible. But by the aid of the microscope we discern
that each tentacle consists of a lengthened fleshy tube, on which
are set at pretty regular intervals thickened semi-rings, or knobs,
very much like the knobs on the horns of an antelope in appearance.
They do not quite encircle the tentacle, and thus one side for the
entire length is smooth and straight. These thickened swellings are
collections of thread-capsules (_cnidæ_), which are packed as close as
they can lie in them, and give to the tentacle that power of adhering
by a touch to any animal whose tissues are penetrable, and of benumbing
and destroying its vitality, in the manner which I have already, on
more than one occasion, alluded to.
I have not yet described the colours of this _Æquorea_; they are,
however, exceedingly lovely and beautiful. The crystalline translucency
of most of these Medusæ, when they are colourless, and of the
colourless parts of such as have bright hues, is exquisite in its
glass-like purity; in this example the whole of the peripheral portion
of the dome is of this hyaline character; but the lower part, which
lies just above the flattened roof, is of a lively azure blue, seen to
great perfection, when the animal is relieved by a dark background:
the colour is gradually lost at about a quarter of an inch from its
bottom. Then the radiating vessels are of a bright rose-colour, drawn
in lines along the colourless surface of the roof; and the marginal
vessel is of the same hue, as are also the four triangular lips of
the polypite, with their ciliary fringes. These, as they depend,
often extending below the level of the margin, waved about in various
directions by the motion of the sea, or by the animal’s own movements,
add greatly to its elegance.