14 BAHIA—BRAZIL, {cuar. 1 
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 regu- 
lating 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 papille, 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 car- 
mine-red fibrous matter, which stains ivory and paper in so 
permanent a manner, that the tint is retained with all its bright- 
ness to the present day: I am quite ignorant of the nature and 
use of this secretion. J have heard from Dr. Allan of Forres, 
that he has frequently found a Diodon, floating alive and dis- 
tended, in the stomach of the shark; and that on several occa- 
sions 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 conferve, in bundles or rafts of from 
twenty to sixty in each. Mr. Berkeley informs me that they are 
the same species (Trichodesmium erythreum) with that found over 
large spaces in the Red Sea, and whence its name of Red Sea is de- 
rived.* 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 conferve. They appear especially com- 
mon in the sea near Australia; and off Cape Leeuwin I found an 
* M. Montagne, in Comptes Rendus, &e. Juillet, 1844; and A: 
Scienc. Nat., Dec. 1844. B ee 5 onal, deg 
