14 
BAHIA—BRAZIL 
CHAP. 
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 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 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 1 8 th .—We sailed from Bahia. A few days after¬ 
wards, when not far distant from the Abrolhos Islets, my atten- 
