"THE VOYAGE OF THE BEAGLE" - читать интересную книгу автора (Darwin Charles)

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 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