1832.\ HABITS OF A BIODON. 13 



Indians say, " the rocks are black ^vhere the waters are white." 

 Here tlie coating is of a rich brown instead of a black colour, 

 and seems to be composed of ferruginous matter alone. Hand 

 specimens fail to gi\e a just idea of these brown burnished 

 stones which glitter in the sun's rays. They occur only within 

 tlie 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 tlie 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 

 understood ; 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 

 antennatus, 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 aerain 

 inmiersed 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 : tlie air is 

 swallowed, and is then forced into the cavity of the body, its 

 return being prevented by a muscular contraction which is exter- 

 nally 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 



