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 18th.--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. [8] 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 the woodcut united together. They
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