THE METEORS OF THE SEA.
As the rushing comets dim the brightest luminaries with their radiance,
so the ocean meteors, the moving _medusæ_, seem to excel in the glory
of their light.
The sea-jellies are among the commonest forms of the seashore. In the
summer months the silvery sands are strewn with their glassy disks;
unattractive then, but, once launched and imbued with life, possessed
of many beauties of form and color. They range in size from those
almost invisible to the naked eye, to giants weighing, it is estimated,
over a ton. Many have a complicated structure; yet, in nearly all, the
solid parts of the animal rarely represents over five per cent of the
whole; and in specimens of a familiar northern kind, _Aurelia_, 95.84
is water. Little opportunity for light in such a creature, one would
say; yet the simple jellies are numbered among the chief illuminators
of the upper region of the ocean. I have observed them in the
Atlantic, the Pacific, and in the Gulf of Mexico, in waters of various
degrees of temperature; but, perhaps, the finest exhibition of their
phosphorescence was seen off Boon Island, on the coast of Maine. The
ocean surface seemed fairly bespangled with these living gems, which
appeared surrounded by a halo of light. Each tentacle seemed to glow
with an intense white heat; and, at a short distance, the streamers
resembled delicate lace, wrought in curious designs. Peering into the
depths, they appeared everywhere, moving in all directions, surrounded
by the mysterious light whose office it is difficult to conjecture.
[Illustration:
PLATE III.
LUMINOUS SEA JELLY.
(_Thaumantius._)
PRUNING-KNIFE FISH.
(_Zanclus._)
LUMINOUS CORAL.]
The vast numbers of _medusæ_, and their importance as light-givers,
may be realized from the remarks of Giglioli, who states that their
light was seen from the “Magenta” over an area of forty-four degrees
of latitude, and for nearly thirty consecutive days. During the day
they sank into the greater depths, at night rising to the surface, and
appearing like moderator lamps. With their long groups of tentacles
trailing behind as they pulsate through the ocean waters, they readily
suggest the title, “Meteors of the Sea.”
With few exceptions, the sea-jellies are light-givers. The giant
_Cyanea_,--one of which was measured by Mrs. Agassiz, and found to
be nearly six feet in diameter, and to have tentacles over one hundred
feet in length--emits a pale, greenish light; and, if the entire mass
is luminous, it must present a wondrous appearance as it moves through
the water, like a gigantic meteor. As large as this giant is, weighing
many hundred pounds, it is produced from a delicate little creature
which would hardly be noticed by the casual observer.
One of the commonest forms along the New-England coast is a diminutive
jelly,[4] seemingly blown in glass by some skilful worker. As it moves
gracefully along, it emits a light of a deep aurelian blue, vast
numbers imparting a metallic glitter to the water.
On some calm night, about a rocky point where the current flows
silently along, myriads of these wondrous forms may be seen passing
in review. Peering down into the depths from our boat, we may see a
pretty, shapely jelly-fish, called _Zygodactyla_, a golden _ignis
fatuus_ of the ocean waters; the _Melicertus_, another of the same
family, surrounded by a golden radiance; and a stately _Rhizostoma_,
which Giglioli observed in fresh or brackish water in Batavia, emitting
a fixed, bluish light; while _Zina_, _Coryne_, _Eucope_ and _Clytia_,
and a host of other exceedingly pretty sea-jellies, add to the glories
of the scene.
The delicate _Thaumantius_ (Plate III., Fig. 3) and Oceanea are
resplendent light-givers. The latter, according to Ehrenberg, being
“surrounded by a shining crown,” while _Pelagia_ illumines the deep sea
by its mystic rays.
Although we have established a rule to refer the most of the technical
names, with the more scientific matter, to the Appendix notes, we are
yet inclined to retain in the text, occasionally, some names which are
especially attractive. Thousands of marine animals have no other name
but the generic ones given them by discoverers; but in many instances
they are pretty, and there is no reason why they should not be used,
as they must become the common name of the object, as well as its
technical one.
Other known light-givers are recorded in the Appendix,[5]--all forms of
the greatest delicacy and beauty.
Of a brilliantly phosphorescent form,[6] Professor Alexander Agassiz
says, “When passing through shoals of these _medusæ_, ranging in
size from a pin’s head to several inches in length, the whole water
becomes so wonderfully luminous that an oar dipped in the water up to
the handle can be seen plainly on dark nights by the light so produced.
The seat of the phosphorescence is confined to the locomotive rows;
and so exceedingly sensitive are they, that the slightest shock is
sufficient to make them visible by the light emitted from the eight
phosphorescent plates.”
[Illustration:
PLATE IV.
LUMINOUS SEA-JELLY AND MOLLUSK.
_Beroe forsakii._ _Cranchia scabra._]
Professor Agassiz also states that the _Lucernaria_[7], a handsome
green sea-jelly, emits a peculiar bluish light of an exceedingly pale
steel color. While all these forms are beautiful individually, their
combined forces produce an array of splendors hardly to be described.
Such pyrotechnic displays of Nature are best observed during the
autumn, when the jellies are wrecked and stranded; the waves hurling
them in, and grinding them up upon the rocks, which appear bathed in
warm, lambent lights.
At Spouting Horn, on the New-England coast, this luminous water
is forced through a small chimney or crevice in the rocks, with a
reverberating roar; sending skyward a column of gleaming water, that
breaks in mid-air and falls in golden spray. In drifting along in
a boat at this time, every movement of the oar produces the most
astonishing results. A slight splash is followed by a blaze of light.
By having a companion keep up a continuous motion of the water, I have
almost been able to read the print of a newspaper by the light of
these disintegrated forms. One of the most striking displays of this
phenomenon I have ever witnessed was at the little port of Ogunquit, Me.
Returning, one dark night, from an off-shore fishing excursion, I saw,
as we approached the harbor, an irregular row of lights, apparently
lanterns in the hands of friends. We hailed, and not until we were
nearly in the surf were we undeceived. The rocks were lined with kelp;
and, when the waves came in, the glowing, sparkling mass of _medusæ_
caught upon the weed, remaining, as the water left it suspended,
a blaze of light, until the next wave broke. My companion, an old
fisherman, had also been deceived by the lights; and we drifted there
for some time watching these strange spectres appear and disappear.
The _medusæ_ differ in their methods of illumination. The _Obelia_, as
a free-swimming disk, is non-luminous; but the stem, or trophosome,
out of which it is developed, has a fluctuating light extending up and
down its surface. In many _medusæ_ the light appears to be confined to
the upper portion of the umbrella, to the tentacles, and to the margin
of the disk; but if an oar is thrust through it, or a freshly stranded
jelly is torn and cut upon the sand, every portion seems to become more
or less luminous.[8]
The little jelly-like creatures called “comb-bearers,” or Ctenophores,
are nearly all wonderfully phosphorescent. Instead of moving as do the
ordinary jelly-fishes, they have rows of comb-like paddles which move
up and down in regular measure as they float along. In the daytime the
little fins gleam with gorgeous iridescent hues; while at night they
are brilliantly luminous, even the eggs and embryos of some emitting
light.
The _Beroë_ (Plate IV., Fig. 1) is the most familiar, but the
Pleurobrachia is the most graceful. Drummond refers to these forms in
the following lines,--
“Shaped as bard’s fancy shapes the small balloon,
To bear some sylph or fay beyond the moon.
From all her bands see lurid fringes play,
That glance and sparkle in the solar ray
With iridescent hues. Now round and round
She whirls and twirls; now mounts, then sinks profound.”
[Illustration:
PLATE V.
VENUS’ GIRDLE.
(_Cestus veneris._)
_Phillerhoe._]
So vast are the numbers of these and other light-givers in the northern
seas, that the olive-green tints of the waters are due to them in the
daytime. Mr. Scoresby, finding sixty-five of them in a cubic inch of
water, summed up the interesting calculation, that, if eighty thousand
persons had commenced at the beginning of the world (he refers to the
popular, not geological, reckoning,) to count, they would barely at the
present time have completed the enumeration of individuals of a single
species found in a cubical mile.
One of the most remarkable of the Ctenophores is the “Venus’ girdle”
(_Cestus veneris_), Plate V., Fig. 1. In shape it differs from all
others of the class, as a comparison between it and the Beroë (Plate
IV.), will show. It resembles in the daytime a silvery ribbon, or
girdle, two or three feet in length, moving through the water by
contractions of the body, rather than by the rows of combs that are
found upon the edges. So delicate is this fragile creature, that it
is almost impossible to remove it intact from the water. The mouth is
in the centre, or equidistant between the ends; and on each side of
it depends a short tentacle protruding from a sac. Opposite the mouth
there is an otocyst, or sense-body. The combs, which are so conspicuous
in other forms, are not so noticeable here, yet are well defined; and
when moving along, and propelled by these gentle undulations, the
_Cestus_ is one of the most beautiful objects of the sea. At night
this wonderful sea-ribbon develops a new charm, emitting, according to
Giglioli, a reddish yellow light of singular brilliancy.
The Ctenophores, from their phosphorescence and great numbers, offer an
interesting field for study. _Pleurobrachia_[9] may be found in myriads
upon our eastern shores in the autumn. _Idya_[10] attracts immediate
attention by its wondrous coloring, having a deep roseate hue. After
death, its phosphorescence appears to be intensified, and much of the
phosphorescent display is due to it. In nearly all the Ctenophores the
light is erratic, flash succeeding flash, and seeming, according to
Giglioli, to reside along the zone covered by the vibrating _cilia_, or
little paddles.
In the interesting group of animals known as _Physophoræ_,[11] or
bubble-bearers, we find many light-givers of most remarkable form,
in their structure reminding one of delicate objects in glass; and,
according to Giglioli, all are more or less luminous. In the harbor of
Gibraltar, he observed several beautiful forms, as _Abyla_, _Diphyes_,
and _Eudoxia_; and in the Atlantic, in the latitude of Rio Janeiro,
_Vogtia_, _Praia_ (Plate VI., Fig. 2), _Abyla_, and _Eudoxia_ were
constantly encountered. These are all so fanciful in design, that they
appear to be veritable fairy ships freighted with color-tints and
gleams of light. Their luminosity is not scattered over the entire
body as in many sea-jellies, but seems confined to fixed points, as
in _Eucope_, a specimen of which, observed in the China Sea, seemed
studded with brilliant emeralds, which appeared as marginal knobs at
the base of the tentacles. In the Pacific, several species of _Diphyes_
have been observed, their zooids[12] brilliantly phosphorescent; but
the hydroids of this group, so far as known, are not luminous.
Many beautiful phosphorescent jellies can be observed, as we drift
along, by using a small glass cylinder. With the finger pressed upon
the top, lower the open end near the little creature, then remove the
finger, when the jelly will be drawn into the improvised aquarium. If
the night is dark, the play about its delicate form will be found a
rare study.
Darwin refers to the beauties of the phosphorescent jellies observed
on one of his collecting-tours. He says, “While sailing a little south
of the Plata on one very dark night, the sea presented a wonderful and
most beautiful spectacle. There was a fresh breeze, and every part
of the surface which during the day is seen as foam now glowed with
a pale light. The vessel drove before her bows two billows of liquid
phosphorus, and in her wake she was followed by a milky train. As far
as the eye reached, the crest of every wave was bright; and the sky
above the horizon, from the reflected glare of these livid flames, was
not so utterly obscure as over the vault of the heavens.... Having used
the net during one night, I allowed it to become partially dry; and
having occasion, twelve hours afterward, to employ it again, I found
the whole surface sparkling as brightly as when first taken out of the
water. It does not appear probable, in this case, that the particles
could have remained so long alive. On one occasion, having kept a
sea-jelly of the genus _Dianæa_ till it was dead, the water in
which it was placed became luminous.... Near Fernando Do Norhona, the
sea gave out light in flashes. The appearance was very similar to that
which might be expected from a large fish moving rapidly through a
luminous fluid. To this cause the sailors attributed it; at the time,
however, I entertained some doubts, on account of the frequency and
rapidity of the flashes.”
To Spallanzani is due the credit of first calling attention to the
phosphorescence of the jelly-fishes or sea-jellies; he having observed
it in the Mediterranean jelly, _Pelagia phosphorea_, which is luminous
over its entire surface. He subsequently made some interesting
experiments with _Aurelia phosphorea_, a jelly-fish similar to one on
our coast, and came to the conclusion that the _light-emitting_ organs
lay in the arms, tentacles, and muscular zone of the body, and cavity
of the stomach; the rest of the animal showing no luminosity. The light
seemed to proceed from a viscous liquid, a secretion which oozed to the
surface. One _Aurelia_ that he squeezed in twenty-seven ounces of milk
rendered the whole so luminous that a letter was read by the light,
this being one of the first practical results of the investigation of
marine phosphorescence. Humboldt experimented with _Aurelia aurita_,
and, having placed it upon a tin plate, observed, that, whenever he
struck it with another metal, the slightest vibration of the tin
rendered the animal completely luminous. He also observed that it
emitted a greater light when in a galvanic circuit.