The Voyage Of The Beagle

Chapter I

 

Porto Praya.
Ribeira Grande.
Atmospheric Dust with Infusoria.
Habits of a Sea-slug and Cuttle-fish.
St. Paul’s Rocks, non-volcanic.
Singular Incrustations.
Insects the first Colonists of Islands.
Fernando Noronha.
Bahia.
Burnished Rocks.
Habits of a Diodon.
Pelagic Confervae and Infusoria.
Causes of discoloured Sea.

ST. JAGO–CAPE DE VERD ISLANDS.

After having been twice driven back by heavy south-western gales,
Her Majesty’s ship “Beagle,” a ten-gun brig, under the command of
Captain Fitz Roy, R.N., sailed from Devonport on the 27th of
December, 1831. The object of the expedition was to complete the
survey of Patagonia and Tierra del Fuego, commenced under Captain
King in 1826 to 1830–to survey the shores of Chile, Peru, and of
some islands in the Pacific–and to carry a chain of chronometrical
measurements round the World. On the 6th of January we reached
Teneriffe, but were prevented landing, by fears of our bringing the
cholera: the next morning we saw the sun rise behind the rugged
outline of the Grand Canary Island, and suddenly illumine the Peak
of Teneriffe, whilst the lower parts were veiled in fleecy clouds.
This was the first of many delightful days never to be forgotten.
On the 16th of January 1832 we anchored at Porto Praya, in St.
Jago, the chief island of the Cape de Verd archipelago.

The neighbourhood of Porto Praya, viewed from the sea, wears a
desolate aspect. The volcanic fires of a past age, and the
scorching heat of a tropical sun, have in most places rendered the
soil unfit for vegetation. The country rises in successive steps of
table-land, interspersed with some truncate conical hills, and the
horizon is bounded by an irregular chain of more lofty mountains.
The scene, as beheld through the hazy atmosphere of this climate,
is one of great interest; if, indeed, a person, fresh from sea, and
who has just walked, for the first time, in a grove of cocoa-nut
trees, can be a judge of anything but his own happiness.

The Cocoa bean is the fruit produced by a cocoa tree that is used to make the different world-famous chocolates. The site web indicates that there are two main species of cocoa

  • The Criollo which is known to be the cocoa princess with excellent flavour and aroma
  • The Forastero which is a higher yielding type

The island
would generally be considered as very uninteresting, but to any one
accustomed only to an English landscape, the novel aspect of an
utterly sterile land possesses a grandeur which more vegetation
might spoil. A single green leaf can scarcely be discovered over
wide tracts of the lava plains; yet flocks of goats, together with
a few cows, contrive to exist. It rains very seldom, but during a
short portion of the year heavy torrents fall, and immediately
afterwards a light vegetation springs out of every crevice. This
soon withers; and upon such naturally formed hay the animals live.
It had not now rained for an entire year. When the island was
discovered, the immediate neighbourhood of Porto Praya was clothed
with trees (1/1. I state this on the authority of Dr. E.
Dieffenbach, in his German translation of the first edition of this
Journal.), the reckless destruction of which has caused here, as at
St. Helena, and at some of the Canary islands, almost entire
sterility. The broad, flat-bottomed valleys, many of which serve
during a few days only in the season as watercourses, are clothed
with thickets of leafless bushes. Few living creatures inhabit
these valleys. The commonest bird is a kingfisher (Dacelo
Iagoensis), which tamely sits on the branches of the castor-oil
plant, and thence darts on grasshoppers and lizards. It is brightly
coloured, but not so beautiful as the European species: in its
flight, manners, and place of habitation, which is generally in the
driest valley, there is also a wide difference.

One day, two of the officers and myself rode to Ribeira Grande, a
village a few miles eastward of Porto Praya. Until we reached the
valley of St. Martin, the country presented its usual dull brown
appearance; but here, a very small rill of water produces a most
refreshing margin of luxuriant vegetation. In the course of an hour
we arrived at Ribeira Grande, and were surprised at the sight of a
large ruined fort and cathedral. This little town, before its
harbour was filled up, was the principal place in the island: it
now presents a melancholy, but very picturesque appearance. Having
procured a black Padre for a guide, and a Spaniard who had served
in the Peninsular war as an interpreter, we visited a collection of
buildings, of which an ancient church formed the principal part. It
is here the governors and captain-generals of the islands have been
buried. Some of the tombstones recorded dates of the sixteenth
century. (1/2. The Cape de Verd Islands were discovered in 1449.
There was a tombstone of a bishop with the date of 1571; and a
crest of a hand and dagger, dated 1497.) The heraldic ornaments
were the only things in this retired place that reminded us of
Europe. The church or chapel formed one side of a quadrangle, in
the middle of which a large clump of bananas were growing. On
another side was a hospital, containing about a dozen
miserable-looking inmates.

We returned to the Vênda to eat our dinners. A considerable number
of men, women, and children, all as black as jet, collected to
watch us. Our companions were extremely merry; and everything we
said or did was followed by their hearty laughter. Before leaving
the town we visited the cathedral. It does not appear so rich as
the smaller church, but boasts of a little organ, which sent forth
singularly inharmonious cries. We presented the black priest with a
few shillings, and the Spaniard, patting him on the head, said,
with much candour, he thought his colour made no great difference.
We then returned, as fast as the ponies would go, to Porto Praya.

Another day we rode to the village of St. Domingo, situated near
the centre of the island. On a small plain which we crossed, a few
stunted acacias were growing; their tops had been bent by the
steady trade-wind, in a singular manner–some of them even at right
angles to their trunks. The direction of the branches was exactly
north-east by north, and south-west by south, and these natural
vanes must indicate the prevailing direction of the force of the
trade-wind. The travelling had made so little impression on the
barren soil, that we here missed our track, and took that to
Fuentes. This we did not find out till we arrived there; and we
were afterwards glad of our mistake. Fuentes is a pretty village,
with a small stream; and everything appeared to prosper well,
excepting, indeed, that which ought to do so most–its inhabitants.
The black children, completely naked, and looking very wretched,
were carrying bundles of firewood half as big as their own bodies.

Near Fuentes we saw a large flock of guinea-fowl–probably fifty or
sixty in number. They were extremely wary, and could not be
approached. They avoided us, like partridges on a rainy day in
September, running with their heads cocked up; and if pursued, they
readily took to the wing.

The scenery of St. Domingo possesses a beauty totally unexpected,
from the prevalent gloomy character of the rest of the island. The
village is situated at the bottom of a valley, bounded by lofty and
jagged walls of stratified lava. The black rocks afford a most
striking contrast with the bright green vegetation, which follows
the banks of a little stream of clear water. It happened to be a
grand feast-day, and the village was full of people. On our return
we overtook a party of about twenty young black girls, dressed in
excellent taste; their black skins and snow-white linen being set
off by coloured turbans and large shawls. As soon as we approached
near, they suddenly all turned round, and covering the path with
their shawls, sung with great energy a wild song, beating time with
their hands upon their legs. We threw them some vintéms, which were
received with screams of laughter, and we left them redoubling the
noise of their song.

One morning the view was singularly clear; the distant mountains
being projected with the sharpest outline, on a heavy bank of dark
blue clouds. Judging from the appearance, and from similar cases in
England, I supposed that the air was saturated with moisture. The
fact, however, turned out quite the contrary. The hygrometer gave a
difference of 29.6 degrees, between the temperature of the air, and
the point at which dew was precipitated. This difference was nearly
double that which I had observed on the previous mornings. This
unusual degree of atmospheric dryness was accompanied by continual
flashes of lightning. Is it not an uncommon case, thus to find a
remarkable degree of aerial transparency with such a state of
weather?

Generally the atmosphere is hazy; and this is caused by the falling
of impalpably fine dust, which was found to have slightly injured
the astronomical instruments. The morning before we anchored at
Porto Praya, I collected a little packet of this brown-coloured
fine dust, which appeared to have been filtered from the wind by
the gauze of the vane at the masthead. Mr. Lyell has also given me
four packets of dust which fell on a vessel a few hundred miles
northward of these islands. Professor Ehrenberg finds that this
dust consists in great part of infusoria with siliceous shields,
and of the siliceous tissue of plants. (1/3. I must take this
opportunity of acknowledging the great kindness with which this
illustrious naturalist has examined many of my specimens. I have
sent (June 1845) a full account of the falling of this dust to the
Geological Society.) In five little packets which I sent him, he
has ascertained no less than sixty-seven different organic forms!
The infusoria, with the exception of two marine species, are all
inhabitants of fresh-water. I have found no less than fifteen
different accounts of dust having fallen on vessels when far out in
the Atlantic. From the direction of the wind whenever it has
fallen, and from its having always fallen during those months when
the harmattan is known to raise clouds of dust high into the
atmosphere, we may feel sure that it all comes from Africa. It is,
however, a very singular fact, that, although Professor Ehrenberg
knows many species of infusoria peculiar to Africa, he finds none
of these in the dust which I sent him. On the other hand, he finds
in it two species which hitherto he knows as living only in South
America. The dust falls in such quantities as to dirty everything
on board, and to hurt people’s eyes; vessels even have run on shore
owing to the obscurity of the atmosphere. It has often fallen on
ships when several hundred, and even more than a thousand miles
from the coast of Africa, and at points sixteen hundred miles
distant in a north and south direction. In some dust which was
collected on a vessel three hundred miles from the land, I was much
surprised to find particles of stone above the thousandth of an
inch square, mixed with finer matter. After this fact one need not
be surprised at the diffusion of the far lighter and smaller
sporules of cryptogamic plants.

The geology of this island is the most interesting part of its
natural history. On entering the harbour, a perfectly horizontal
white band in the face of the sea cliff, may be seen running for
some miles along the coast, and at the height of about forty-five
feet above the water. Upon examination, this white stratum is found
to consist of calcareous matter, with numerous shells embedded,
most or all of which now exist on the neighbouring coast. It rests
on ancient volcanic rocks, and has been covered by a stream of
basalt, which must have entered the sea when the white shelly bed
was lying at the bottom. It is interesting to trace the changes,
produced by the heat of the overlying lava, on the friable mass,
which in parts has been converted into a crystalline limestone, and
in other parts into a compact spotted stone. Where the lime has
been caught up by the scoriaceous fragments of the lower surface of
the stream, it is converted into groups of beautifully radiated
fibres resembling arragonite. The beds of lava rise in successive
gently-sloping plains, towards the interior, whence the deluges of
melted stone have originally proceeded. Within historical times no
signs of volcanic activity have, I believe, been manifested in any
part of St. Jago. Even the form of a crater can but rarely be
discovered on the summits of the many red cindery hills; yet the
more recent streams can be distinguished on the coast, forming
lines of cliffs of less height, but stretching out in advance of
those belonging to an older series: the height of the cliffs thus
affording a rude measure of the age of the streams.

During our stay, I observed the habits of some marine animals. A
large Aplysia is very common. This sea-slug is about five inches
long; and is of a dirty yellowish colour, veined with purple. On
each side of the lower surface, or foot, there is a broad membrane,
which appears sometimes to act as a ventilator, in causing a
current of water to flow over the dorsal branchiae or lungs. It
feeds on the delicate seaweeds which grow among the stones in muddy
and shallow water; and I found in its stomach several small
pebbles, as in the gizzard of a bird. This slug, when disturbed,
emits a very fine purplish-red fluid, which stains the water for
the space of a foot around. Besides this means of defence, an acrid
secretion, which is spread over its body, causes a sharp, stinging
sensation, similar to that produced by the Physalia, or Portuguese
man-of-war.

I was much interested, on several occasions, by watching the habits
of an Octopus, or cuttle-fish. Although common in the pools of
water left by the retiring tide, these animals were not easily
caught. By means of their long arms and suckers, they could drag
their bodies into very narrow crevices; and when thus fixed, it
required great force to remove them. At other times they darted
tail first, with the rapidity of an arrow, from one side of the
pool to the other, at the same instant discolouring the water with
a dark chestnut-brown ink. These animals also escape detection by a
very extraordinary, chameleon-like power of changing their colour.
They appear to vary their tints according to the nature of the
ground over which they pass: when in deep water, their general
shade was brownish purple, but when placed on the land, or in
shallow water, this dark tint changed into one of a yellowish
green. The colour, examined more carefully, was a French grey, with
numerous minute spots of bright yellow: the former of these varied
in intensity; the latter entirely disappeared and appeared again by
turns. These changes were effected in such a manner that clouds,
varying in tint between a hyacinth red and a chestnut-brown, were
continually passing over the body. (1/4. So named according to
Patrick Symes’s nomenclature.) Any part, being subjected to a
slight shock of galvanism, became almost black: a similar effect,
but in a less degree, was produced by scratching the skin with a
needle. These clouds, or blushes as they may be called, are said to
be produced by the alternate expansion and contraction of minute
vesicles containing variously coloured fluids. (1/5. See
“Encyclopedia of Anatomy and Physiology” article “Cephalopoda.”)

This cuttle-fish displayed its chameleon-like power both during the
act of swimming and whilst remaining stationary at the bottom. I
was much amused by the various arts to escape detection used by one
individual, which seemed fully aware that I was watching it.
Remaining for a time motionless, it would then stealthily advance
an inch or two, like a cat after a mouse; sometimes changing its
colour: it thus proceeded, till having gained a deeper part, it
darted away, leaving a dusky train of ink to hide the hole into
which it had crawled.

While looking for marine animals, with my head about two feet above
the rocky shore, I was more than once saluted by a jet of water,
accompanied by a slight grating noise. At first I could not think
what it was, but afterwards I found out that it was this
cuttle-fish, which, though concealed in a hole, thus often led me
to its discovery. That it possesses the power of ejecting water
there is no doubt, and it appeared to me that it could certainly
take good aim by directing the tube or siphon on the under side of
its body. From the difficulty which these animals have in carrying
their heads, they cannot crawl with ease when placed on the ground.
I observed that one which I kept in the cabin was slightly
phosphorescent in the dark.

ST. PAUL’S ROCKS.

In crossing the Atlantic we hove-to, during the morning of February
16th, 1832, close to the island of St. Paul’s. This cluster of
rocks is situated in 0 degrees 58′ north latitude, and 29 degrees
15′ west longitude. It is 540 miles distant from the coast of
America, and 350 from the island of Fernando Noronha. The highest
point is only fifty feet above the level of the sea, and the entire
circumference is under three-quarters of a mile. This small point
rises abruptly out of the depths of the ocean. Its mineralogical
constitution is not simple; in some parts the rock is of a cherty,
in others of a feldspathic nature, including thin veins of
serpentine. It is a remarkable fact that all the many small
islands, lying far from any continent, in the Pacific, Indian, and
Atlantic Oceans, with the exception of the Seychelles and this
little point of rock, are, I believe, composed either of coral or
of erupted matter. The volcanic nature of these oceanic islands is
evidently an extension of that law, and the effect of those same
causes, whether chemical or mechanical, from which it results that
a vast majority of the volcanoes now in action stand either near
sea-coasts or as islands in the midst of the sea.

(PLATE 4. INCRUSTATION OF SHELLY SAND.)

The rocks of St. Paul appear from a distance of a brilliantly white
colour. This is partly owing to the dung of a vast multitude of
seafowl, and partly to a coating of a hard glossy substance with a
pearly lustre, which is intimately united to the surface of the
rocks. This, when examined with a lens, is found to consist of
numerous exceedingly thin layers, its total thickness being about
the tenth of an inch. It contains much animal matter, and its
origin, no doubt, is due to the action of the rain or spray on the
birds’ dung. Below some small masses of guano at Ascension, and on
the Abrolhos Islets, I found certain stalactitic branching bodies,
formed apparently in the same manner as the thin white coating on
these rocks. The branching bodies so closely resembled in general
appearance certain nulliporae (a family of hard calcareous
sea-plants), that in lately looking hastily over my collection I
did not perceive the difference. The globular extremities of the
branches are of a pearly texture, like the enamel of teeth, but so
hard as just to scratch plate-glass. I may here mention, that on a
part of the coast of Ascension, where there is a vast accumulation
of shelly sand, an incrustation is deposited on the tidal rocks, by
the water of the sea, resembling, as represented in Plate 4,
certain cryptogamic plants (Marchantiae) often seen on damp walls.
The surface of the fronds is beautifully glossy; and those parts
formed where fully exposed to the light, are of a jet black colour,
but those shaded under ledges are only grey. I have shown specimens
of this incrustation to several geologists, and they all thought
that they were of volcanic or igneous origin! In its hardness and
translucency–in its polish, equal to that of the finest
oliva-shell–in the bad smell given out, and loss of colour under
the blowpipe–it shows a close similarity with living sea-shells.
Moreover in sea-shells, it is known that the parts habitually
covered and shaded by the mantle of the animal, are of a paler
colour than those fully exposed to the light, just as is the case
with this incrustation. When we remember that lime, either as a
phosphate or carbonate, enters into the composition of the hard
parts, such as bones and shells, of all living animals, it is an
interesting physiological fact to find substances harder than the
enamel of teeth, and coloured surfaces as well polished as those of
a fresh shell, re-formed through inorganic means from dead organic
matter–mocking, also, in shape, some of the lower vegetable
productions. (1/6. Mr. Horner and Sir David Brewster have described
(“Philosophical Transactions” 1836 page 65) a singular “artificial
substance resembling shell.” It is deposited in fine, transparent,
highly polished, brown-coloured laminae, possessing peculiar
optical properties, on the inside of a vessel, in which cloth,
first prepared with glue and then with lime, is made to revolve
rapidly in water. It is much softer, more transparent, and contains
more animal matter, than the natural incrustation at Ascension; but
we here again see the strong tendency which carbonate of lime and
animal matter evince to form a solid substance allied to shell.)

We found on St. Paul’s only two kinds of birds–the booby and the
noddy. The former is a species of gannet, and the latter a tern.
Both are of a tame and stupid disposition, and are so unaccustomed
to visitors, that I could have killed any number of them with my
geological hammer. The booby lays her eggs on the bare rock; but
the tern makes a very simple nest with seaweed. By the side of many
of these nests a small flying-fish was placed; which I suppose, had
been brought by the male bird for its partner. It was amusing to
watch how quickly a large and active crab (Graspus), which inhabits
the crevices of the rock, stole the fish from the side of the nest,
as soon as we had disturbed the parent birds. Sir W. Symonds, one
of the few persons who have landed here, informs me that he saw the
crabs dragging even the young birds out of their nests, and
devouring them. Not a single plant, not even a lichen, grows on
this islet; yet it is inhabited by several insects and spiders. The
following list completes, I believe, the terrestrial fauna: a fly
(Olfersia) living on the booby, and a tick which must have come
here as a parasite on the birds; a small brown moth, belonging to a
genus that feeds on feathers; a beetle (Quedius) and a woodlouse
from beneath the dung; and lastly, numerous spiders, which I
suppose prey on these small attendants and scavengers of the
waterfowl. The often-repeated description of the stately palm and
other noble tropical plants, then birds, and lastly man, taking
possession of the coral islets as soon as formed, in the Pacific,
is probably not quite correct; I fear it destroys the poetry of
this story, that feather and dirt-feeding and parasitic insects and
spiders should be the first inhabitants of newly formed oceanic
land.

The smallest rock in the tropical seas, by giving a foundation for
the growth of innumerable kinds of seaweed and compound animals,
supports likewise a large number of fish. The sharks and the seamen
in the boats maintained a constant struggle which should secure the
greater share of the prey caught by the fishing-lines. I have heard
that a rock near the Bermudas, lying many miles out at sea, and at
a considerable depth, was first discovered by the circumstance of
fish having been observed in the neighbourhood.

FERNANDO NORONHA, FEBRUARY 20, 1832.

As far as I was enabled to observe, during the few hours we stayed
at this place, the constitution of the island is volcanic, but
probably not of a recent date. The most remarkable feature is a
conical hill, about one thousand feet high, the upper part of which
is exceedingly steep, and on one side overhangs its base. The rock
is phonolite, and is divided into irregular columns. On viewing one
of these isolated masses, at first one is inclined to believe that
it has been suddenly pushed up in a semi-fluid state. At St.
Helena, however, I ascertained that some pinnacles, of a nearly
similar figure and constitution, had been formed by the injection
of melted rock into yielding strata, which thus had formed the
moulds for these gigantic obelisks. The whole island is covered
with wood; but from the dryness of the climate there is no
appearance of luxuriance. Half-way up the mountain some great
masses of the columnar rock, shaded by laurel-like trees, and
ornamented by others covered with fine pink flowers but without a
single leaf, gave a pleasing effect to the nearer parts of the
scenery.

BAHIA, OR SAN SALVADOR. BRAZIL, FEBRUARY 29, 1832.

The day has past delightfully. Delight itself, however, is a weak
term to express the feelings of a naturalist who, for the first
time, has wandered by himself in a Brazilian forest. The elegance
of the grasses, the novelty of the parasitical plants, the beauty
of the flowers, the glossy green of the foliage, but above all the
general luxuriance of the vegetation, filled me with admiration. A
most paradoxical mixture of sound and silence pervades the shady
parts of the wood. The noise from the insects is so loud, that it
may be heard even in a vessel anchored several hundred yards from
the shore; yet within the recesses of the forest a universal
silence appears to reign. To a person fond of natural history, such
a day as this brings with it a deeper pleasure than he can ever
hope to experience again. After wandering about for some hours, I
returned to the landing-place; but, before reaching it, I was
overtaken by a tropical storm. I tried to find shelter under a
tree, which was so thick that it would never have been penetrated
by common English rain; but here, in a couple of minutes, a little
torrent flowed down the trunk. It is to this violence of the rain
that we must attribute the verdure at the bottom of the thickest
woods: if the showers were like those of a colder clime, the
greater part would be absorbed or evaporated before it reached the
ground. I will not at present attempt to describe the gaudy scenery
of this noble bay, because, in our homeward voyage, we called here
a second time, and I shall then have occasion to remark on it.

Along the whole coast of Brazil, for a length of at least 2000
miles, and certainly for a considerable space inland, wherever
solid rock occurs, it belongs to a granitic formation. The
circumstance of this enormous area being constituted of materials
which most geologists believe to have been crystallised when heated
under pressure, gives rise to many curious reflections. Was this
effect produced beneath the depths of a profound ocean? or did a
covering of strata formerly extend over it, which has since been
removed? Can we believe that any power, acting for a time short of
infinity, could have denuded the granite over so many thousand
square leagues?

On a point not far from the city, where a rivulet entered the sea,
I observed a fact connected with a subject discussed by Humboldt.
(1/7. “Personal Narrative” volume 5 part 1 page 18.) At the
cataracts of the great rivers Orinoco, Nile, and Congo, the
syenitic rocks are coated by a black substance, appearing as if
they had been polished with plumbago. The layer is of extreme
thinness; and on analysis by Berzelius it was found to consist of
the oxides of manganese and iron. In the Orinoco it occurs on the
rocks periodically washed by the floods, and in those parts alone
where the stream is rapid; or, as the Indians say, “the rocks are
black where the waters are white.” Here the coating is of a rich
brown instead of a black colour, and seems to be composed of
ferruginous matter alone. Hand specimens fail to give a just idea
of these brown burnished stones which glitter in the sun’s rays.
They occur only within the limits of the tidal waves; and as the
rivulet slowly trickles down, the surf must supply the polishing
power of the cataracts in the great rivers. In like manner, the
rise and fall of the tide probably answer to the periodical
inundations; and thus the same effects are produced under
apparently different but really similar circumstances. The origin,
however, of these coatings of metallic oxides, which seem as if
cemented to the rocks, is not understood; and no reason, I believe,
can be assigned for their thickness remaining the same.

(PLATE 5. DIODON MACULATUS (DISTENDED AND CONTRACTED).)

One day I was amused by watching the habits of the Diodon
antennatus, which was caught swimming near the shore. This fish,
with its flabby skin, is well known to possess the singular power
of distending itself into a nearly spherical form. After having
been taken out of water for a short time, and then again immersed
in it, a considerable quantity both of water and air is absorbed by
the mouth, and perhaps likewise by the branchial orifices. This
process is effected by two methods: the air is swallowed, and is
then forced into the cavity of the body, its return being prevented
by a muscular contraction which is externally visible: but the
water enters in a gentle stream through the mouth, which is kept
wide open and motionless; this latter action must, therefore,
depend on suction. The skin about the abdomen is much looser than
that on the back; hence, during the inflation, the lower surface
becomes far more distended than the upper; and the fish, in
consequence, floats with its back downwards. Cuvier doubts whether
the Diodon in this position is able to swim; but not only can it
thus move forward in a straight line, but it can turn round to
either side. This latter movement is effected solely by the aid of
the pectoral fins; the tail being collapsed and not used. From the
body being buoyed up with so much air, the branchial openings are
out of water, but a stream drawn in by the mouth constantly flows
through them.

The fish, having remained in this distended state for a short time,
generally expelled the air and water with considerable force from
the branchial apertures and mouth. It could emit, at will, a
certain portion of the water, and it appears, therefore probable
that this fluid is taken in partly for the sake of regulating its
specific gravity. This Diodon possessed several means of defence.
It could give a severe bite, and could eject water from its mouth
to some distance, at the same time making a curious noise by the
movement of its jaws. By the inflation of its body, the papillae,
with which the skin is covered, become erect and pointed. But the
most curious circumstance is, that it secretes from the skin of its
belly, when handled, a most beautiful carmine-red fibrous matter,
which stains ivory and paper in so permanent a manner, that the
tint is retained with all its brightness to the present day: I am
quite ignorant of the nature and use of this secretion. I have
heard from Dr. Allan of Forres, that he has frequently found a
Diodon, floating alive and distended, in the stomach of the shark;
and that on several occasions he has known it eat its way, not only
through the coats of the stomach, but through the sides of the
monster, which has thus been killed. Who would ever have imagined
that a little soft fish could have destroyed the great and savage
shark?

MARCH 18, 1832.

(PLATE 6. PELAGIC CONFERVAE.)

We sailed from Bahia. A few days afterwards, when not far distant
from the Abrolhos Islets, my attention was called to a
reddish-brown appearance in the sea. The whole surface of the
water, as it appeared under a weak lens, seemed as if covered by
chopped bits of hay, with their ends jagged. These are minute
cylindrical confervae, in bundles or rafts of from twenty to sixty
in each. Mr. Berkeley informs me that they are the same species
(Trichodesmium erythraeum) with that found over large spaces in the
Red Sea, and whence its name of Red Sea is derived. (1/8. M.
Montagne in “Comptes Rendus” etc. Juillet 1844; and “Annales des
Sciences Naturelles” December 1844.) Their numbers must be
infinite: the ship passed through several bands of them, one of
which was about ten yards wide, and, judging from the mud-like
colour of the water, at least two and a half miles long. 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 Plate 6
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 here add 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. (1/9. M. Lesson “Voyage de la Coquille” tome 1
page 255, mentions red water off Lima, apparently produced by the
same cause. Peron, the distinguished naturalist, in the “Voyage aux
Terres Australes,” gives no less than twelve references to voyagers
who have alluded to the discoloured waters of the sea (volume 2
page 239). To the references given by Peron may be added,
Humboldt’s “Personal Narrative” volume 6 page 804; Flinder’s
“Voyage” volume 1 page 92; Labillardière, volume 1 page 287;
Ulloa’s “Voyage”; “Voyage of the Astrolabe and of the Coquille”;
Captain King’s “Survey of Australia” etc.)

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 embedded: 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 direction of the bands
indicates 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 carcass of some whale, which probably was floating at no
great distance. I do not here mention the minute gelatinous
particles, hereafter to be referred to, which are frequently
dispersed throughout the water, for they are not sufficiently
abundant to create any change of colour.

There are two circumstances in the above accounts which appear
remarkable: first, how do the various bodies which form the bands
with defined edges keep together? In the case of the prawn-like
crabs, their movements were as coinstantaneous as in a regiment of
soldiers; but this cannot happen from anything like voluntary
action with the ovules, or the confervae, nor is it probable among
the infusoria. Secondly, what causes the length and narrowness of
the bands? The appearance so much resembles that which may be seen
in every torrent, where the stream uncoils into long streaks the
froth collected in the eddies, that I must attribute the effect to
a similar action either of the currents of the air or sea. Under
this supposition we must believe that the various organised bodies
are produced in certain favourable places, and are thence removed
by the set of either wind or water. I confess, however, there is a
very great difficulty in imagining any one spot to be the
birthplace of the millions of millions of animalcula and confervae:
for whence come the germs at such points?–the parent bodies having
been distributed by the winds and waves over the immense ocean. But
on no other hypothesis can I understand their linear grouping. I
may add that Scoresby remarks that green water abounding with
pelagic animals is invariably found in a certain part of the Arctic
Sea.

(PLATE 7. CATAMARAN (BAHIA).)

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