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 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