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KAMAKICHI KISHINOUYE : 
posterior end of the principal cavity. At the anterior end of this upper 
accessory cavity a vein pours to a segmentary vein. In immature tunnies 
the air-bladder is very small, and almost collapsed. The air-bladder of this 
species has a pair of slight swellings along the anterior side. 
In Parathunnus mebachi the air-bladder is a little narrower thin the roof 
of the abdominal cavity ; but occupies the entire length of the cavity, at the 
anterior end the air-bladder is divided into two large coeca, by the dorsal 
aorta in the middle, and is separated by the cutaneous arteries from the principal 
cavity. The internal wall is finely reticulated. 
In Neotkwinus macropterus the air-bladder is narrow, and is protected by 
a very thick mass of connective tissue from the ventral side. Tliis thick mass 
of connective tissue is utilized as a material in making glue. On the middle 
of the dorsal wall a large vein is found with radiating venules from all sides. 
The red gland is developed at the anterior part of the air-bladder, near the 
point where the artery for the air-bladder enters. The air-bladder of the Scom- 
bridae and Cybiidae receives blood from the dorsal aorta at several points, and 
pours its venous blood to the posterior cardinal vein at several spots ; but in 
the Plecostei the arterial blood is received from a special branch of an artery, 
running along the right hand side of the stomach, and the venous blood pours 
to the caudal or the posterior cardinal vein through a segmental vein. Thus 
the arterial system of the air-bladder belongs to the axial system in the Scom- 
bridae and Cybiidae, but to the visceral system in the Plecostei. 
DIGESTIVE SYSTEM. 
The moutli-cavity is black in the Scombridae, black or greyish in the 
Cybiidae and Thunnidae, and silvery or colourless in the Katsuwonidae. The 
tongue is small, narrow, and black in colour, and far beliind the symphysis of 
the lower jaw in the Scombridae ; broad, flat, and generally greyish in the Cybi¬ 
idae ; greyish in the Thunnidae ; and silvery white, medium in size, and the 
membrane at the lateral margins is turned upward in the Katsuwonidae. The 
surface of the tongue is granulated in the genus Scomber, armed with villous 
teeth in Gymnosarda and Thunnidae, and quite smooth in Acanthocybium, in 
many species of the genus Gybium, and in the fishes of the Katsuwonidae. 
The development of the ^ill-rakers on the branchial arches has a close 
