In Almost Every Long
Voyage Some Account Is Given Of These Confervae.
They appear
especially common in the sea near Australia; and off
Cape Leeuwin I found an allied but smaller and apparently
different species.
Captain Cook, in his third voyage, remarks,
that the sailors gave to this appearance the name of
sea-sawdust.
Near Keeling Atoll, in the Indian Ocean, I observed
many little masses of confervae a few inches square, consisting
of long cylindrical threads of excessive thinness, so as
to be barely visible to the naked eye, mingled with other
rather larger bodies, finely conical at both ends. Two of
these are shown in the woodcut united together. They vary
in length from .04 to .06, and even to .08 of an inch in
length; and in diameter from .006 to .008 of an inch. Near
one extremity of the cylindrical part, a green septum, formed
of granular matter, and thickest in the middle, may generally
be seen. This, I believe, is the bottom of a most delicate,
colourless sac, composed of a pulpy substance, which lines
the exterior case, but does not extend within the extreme
conical points. In some specimens, small but perfect spheres
of brownish granular matter supplied the
places of the septa; and I observed the curious process by
which they were produced. The pulpy matter of the internal
coating suddenly grouped itself into lines, some of which
assumed a form radiating from a common centre; it then
continued, with an irregular and rapid movement, to contract
itself, so that in the course of a second the whole was
united into a perfect little sphere, which occupied the
position of the septum at one end of the now quite hollow case.
The formation of the granular sphere was hastened by any
accidental injury. I may add, that frequently a pair of these
bodies were attached to each other, as represented above,
cone beside cone, at that end where the septum occurs.
I will add here a few other observations connected with
the discoloration of the sea from organic causes. On the
coast of Chile, a few leagues north of Concepcion, the Beagle
one day passed through great bands of muddy water, exactly
like that of a swollen river; and again, a degree south of
Valparaiso, when fifty miles from the land, the same appearance
was still more extensive. Some of the water placed
in a glass was of a pale reddish tint; and, examined under
a microscope, was seen to swarm with minute animalcula
darting about, and often exploding. Their shape is oval,
and contracted in the middle by a ring of vibrating curved
ciliae. It was, however, very difficult to examine them with
care, for almost the instant motion ceased, even while crossing
the field of vision, their bodies burst. Sometimes both
ends burst at once, sometimes only one, and a quantity of
coarse, brownish, granular matter was ejected. The animal
an instant before bursting expanded to half again its natural
size; and the explosion took place about fifteen seconds
after the rapid progressive motion had ceased: in a few
cases it was preceded for a short interval by a rotatory
movement on the longer axis. About two minutes after any
number were isolated in a drop of water, they thus perished.
The animals move with the narrow apex forwards, by the
aid of their vibratory ciliae, and generally by rapid starts.
They are exceedingly minute, and quite invisible to the
naked eye, only covering a space equal to the square of the
thousandth of an inch. Their numbers were infinite; for
the smallest drop of water which I could remove contained
very many. In one day we passed through two spaces of
water thus stained, one of which alone must have extended
over several square miles. What incalculable numbers of
these microscopical animals! The colour of the water, as
seen at some distance, was like that of a river which has
flowed through a red clay district, but under the shade of
the vessel's side it was quite as dark as chocolate. The line
where the red and blue water joined was distinctly defined.
The weather for some days previously had been calm, and the
ocean abounded, to an unusual degree, with living creatures. [9]
In the sea around Tierra del Fuego, and at no great distance
from the land, I have seen narrow lines of water of a
bright red colour, from the number of crustacea, which
somewhat resemble in form large prawns. The sealers call
them whale-food. Whether whales feed on them I do not
know; but terns, cormorants, and immense herds of great
unwieldy seals derive, on some parts of the coast, their
chief sustenance from these swimming crabs. Seamen
invariably attribute the discoloration of the water to spawn;
but I found this to be the case only on one occasion. At
the distance of several leagues from the Archipelago of the
Galapagos, the ship sailed through three strips of a dark
yellowish, or mud-like water; these strips were some miles
long, but only a few yards wide, and they were separated
from the surrounding water by a sinuous yet distinct margin.
The colour was caused by little gelatinous balls, about
the fifth of an inch in diameter, in which numerous minute
spherical ovules were imbedded: they were of two distinct
kinds, one being of a reddish colour and of a different shape
from the other. I cannot form a conjecture as to what two
kinds of animals these belonged. Captain Colnett remarks,
that this appearance is very common among the Galapagos
Islands, and that the directions of the bands indicate that
of the currents; in the described case, however, the line was
caused by the wind. The only other appearance which I
have to notice, is a thin oily coat on the water which displays
iridescent colours. I saw a considerable tract of the
ocean thus covered on the coast of Brazil; the seamen
attributed it to the putrefying carcase of some whale, which
probably was floating at no great distance.
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