PLECTOGNATES. 
of the Diodon ( Ckilomycterus ) antennatus, which was 
caught swimming near the shore. This fish 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 meth- 
ods; 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, I observed, 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 sur- 
face 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 were 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 
month. 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 per- 
manent a manner, that the tint is retained with all its 
brightness to the present day. I am quite ignorant of 
the nature and use of this secretion. I have heard 
(>21 
from Dr. Allan of Forres, that he has frequently found 
a Diodon, floating alive and distended, in the stomach 
of the Shark; and that on several occasions he has known 
it eat its way, not only through the coats of the sto- 
mach, but through the sides of the monster, which has 
thus been killed. Who would ever have imagined that 
a little soft fish could have destroyed the great and 
savage Shark?” 
The power here mentioned by Darwin, that of pro- 
ducing sounds, is one of the faculties highly characteristic 
of these fishes. The Plectognates have long been known 
as the most assiduous musicians of the ocean. Now it 
is the jaws, now the articular surfaces of the spinous 
rays in the dorsal or ventral fins, where these fins con- 
tain such rays, that make a snapping, ringing, grating, 
or laughing noise"; now it is the hissing sound of water 
and air driven out of the body; now it is the air- 
bladder whose vibrations may be distinctly heard like 
the beating of a drum 4 . For this purpose the air-bladder 
is attached, in the drumming Balistoids, to the shoulder- 
girdle on each side and to special, large dermal plates 
just above the upper angle of the pectoral tin. By the 
quivering movements that accompany the violent con- 
traction (ef. above, p. 193) of the ventral parts of the 
lateral muscles, the postclavicular bones, which are in- 
serted in these muscles, are set in a vibrating motion 
which is transferred to the wall of the air-bladder and 
to the air contained therein, from which the sound is 
transmitted to the said osseous plates in the skin above 
the angle of the pectoral fin, and through their medium 
to the outer world. All the snapping, ringing, grating, 
laughing, or hissing sounds are probably intended, here 
as in other fishes which have this power, in the first 
place to frighten away some approaching foe. The 
notes or drumming noises of the air-bladder may also 
conduce to the same result, or may be produced by 
the death-throes of the fish. But, as Sorensen has 
remarked, the sonorous tones that compose the song 
of these fishes, undoubtedly serve in other cases, espe- 
cially during the spawning-season, as call-notes. 
Cuvier 1 ' divided the Plectognates into two families, 
the first with free teeth in the jaws and usually with 
hard (plate-like) dermal covering — hence the name of 
les Sclerodermes, from Gxfajpos, hard and deQ/ucc, skin 
— the second with the jaw-teeth confluent and forming 
“ Cf. Sorensen, Om Lydorganer hos Fishe , Kjabenhavn, 1884. 
6 Cf. Mobius, Balistes aculeatus , ein trommelnder Fisch , Stzber. Akad. Wiss. Berk 18 89, p. 999. 
c Regne Animal !, ed. 1, tom. II, pp. 145 and 149; ed. 2, tom. II, pp. 365 and 371. 
