14 BAHIA— BRAZIL 



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 i 8///. — We sailed from Bahia. A few days after- 

 wards, when not far distant from the Abrolhos Islets, my atten- 



