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