10 HABITS OF A DIODON. [CHAP. I. 



and iron. In the Orinoco it occurs on the rocks periodically vyashed 

 by the floods, and in those parts alone where the stream is rapid ; or, 

 as the Indians say, "the rocks are black where the waters are white." 

 Here the coating is of a rich brown instead of a black colour, and seems 

 to be composed of ferruginous matter alone. Hand specimens fail to 

 give a just idea of these brown burnished stones which glitter in the 

 sun's rays. They occur only within the limits of the tidal waves ; and 

 as the rivulet slowly trickles down, the surf must supply the polishing 

 power of the cataracts in the great rivers. In like manner, the rise and 

 fall of the tide probably answer to the periodical inundations ; and thus 

 the same effects are produced under apparently different but really 

 similar circumstances. The origin, however, of these coatings of 

 metallic oxides, which seem as if cemented to the rocks, is not under- 

 stood ; and no reason, I believe, can be assigned for their thickness 

 remaining the same. 



One day I was amused by watching the habits of the Diodon anten- 

 natus, which was caught swimming near the shore. This fish, with its 

 flabby skin, is well known to possess the singular power of distending 

 itself into a nearly spherical form. After having been taken out of 

 water for a short time, and then again immersed in it, a considerable 

 quantity both of water and air is absorbed by the mouth, and perhaps 

 likewise by the branchial orifices. This process is effected by two 

 methods ; the air is swallowed, and is then forced into the cavity of 

 the body, its 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 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 



