COMPARATIVE STUDY OF SCOMBROID FISHES. 
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difficult to understand that Acanthocybium which is always found near the 
surface has a well developed air-bladder, while Cybium niphonium which has 
a rather wide range of vertical distribution lacks it. The air-bladder is more 
or less fusiform, and generally thickened at the anterior part. 
In the Scombridae the air-bladder is generally present, being absent in 
Scomber scombrus only. In Scomber japonicus the air-bladder is fusiform, 
naiTow and pointed at both ends. It occupies a little more than half the 
length of the abdominal cavity. It3 wall is very thin. 
In the Cybiidae the air-bladder is not found in Cybium niphonium, C. 
lioreanum, and Sarcla orientalis. In Gymnosarda nuda the air-bladder is 
large and thick-walled. 
Fig. L. Air-bladder of tunnies. 1, Thunnus germo (dorsal and side views) ; 
2, Thunnus orientalis (dorsal and side views); 3, Parathunnus mebachi (dorsal 
and side views) ; i, Neothunnus macropterus (ventral view). 
In the Thunnidae the development of the ah*-bladder is very interesting. 
In Thunnus germo the air-bladder is narrow, but long, running the whole 
length of the abdominal cavity, and has a median dorsal swelling at the 
anterior end. In Thunnus orientalis the air-bladder is triangular, very wide, and 
straight at the anterior end, occupying the entire breadth of the abdominal cavity, 
but it is short, and becomes gradually narrow behind, pointed at the posterior 
end. It is a little longer than half the length of the abdominal cavity. The 
external wall is uniformly thin. The internal wall is finely reticulated. At 
the middle of the roof of the air-bladder, there is a large round hole, which 
leads to an accessory conical cavity, extending horn the hole behind to the 
