1832.] HABITS OF A. DIODON. 13 
Indians say, ‘‘ the rocks are black where the waters are white.” 
Here the coating is ofa 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 
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 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 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 
