(PLATE 5. DIODON MACULATUS (DISTENDED AND CONTRACTED).)
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.
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