48 THE GOLDFISH AND ITS CULTURE. 
need something to keep them apart, so that their surfaces may be 
exposed and perform their functions properly, otherwise they would 
close together, the blood-vessels would cease to absorb the oxygen, 
resulting, of course, in the death of the fish. It is necessary, then, 
that a stream of water should constantly flow through them, as it 
does, the absorption of oxygen then going on as nature intended, 
The feart of the fish lies just behind the head and between the 
gills (fig. g.). It is a muscular organ consisting of three parts, an 
auricle, a ventricle, and an arterial bulb, The venous or stale blood 
is pumped into the gills by the heart, where it receives a fresh supply 
of oxygen. From the gills it is sent to an arterial trunk, lying along 
the under side of the vertebral column, (fig. h.) from which it is 
distributed all over the body of the fish. 
As fish have no lungs, they can not possess a voice. 
The goldfish is supplied with a divided as7-dladder (fig, i. i.) which 
can be filled or emptied at will. This bladder is a sac formed of a 
tough membrane, and is situated between the spinal column and the 
stomach, (fig, k.) 
It appears that the air-bladder is either for the purpose of increas- 
ing the weight of the fish when empty, and decreasing it when full, 
thus exercising a modifying influence upon the weight of the fish 
when compared with that of the water. 
The eves of the goldfish are well developed, but so far as hearing 
is concerned, opinions differ, and the question is still disputed. It 
may be stated that if fish hear at all, it is with great difficulty. 
It is the custom in some places where fish are kept to call them 
to their feeding place by the tolling of a bell, and they come, but it 
is a question whether they come because they hear the sownd, or 
that they see the motion of the person ringing the bell, or that of 
the bell itself; this, then, can not be cited in proof of the theory 
that they hear. 
