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KAMAK1CAI KISHINOUYE : 
but in the Cybiiclae the cavity is more or less separated from the vertebral 
column, from the development of the haemal processes in many precaudal 
vertebrae. In the the Plecostei the coelomic cavity is low and narrow, as the 
haemal process of precaudal vertebrae is much better developed than in the 
Cybiidae. The height of the cavity is less than its breadth, and its roof is 
flat or convex, thatched with a broad proximal portion of ribs, and protected 
by the peritoneum, composed of thick bundles of connective tissue arising from 
the distal end of the precaudal haemal spines, and interwoven with each other 
at their root. These bundles of connective tissue are inserted at the ventral 
median line of the cavity, here too, their ends are interwoven. Generally 
speaking the visceral cavity of the scombroid fishes does not extend to the 
caudal portion, though some posterior ribs push their way into the lateral 
muscle, beyond the peritoneum, and lie on each side of the interhaemals. Thus 
the length of the abdominal cavity may approximately be known by measuring 
the distance of the anus from the gill-slit. In the genus Auxis, however, the 
genital gland extends beyond the origin of the anal, and grasps the inter- 
haemals of the fin from both sides. Thus the abdominal cavity is also extended 
backward beyond the anus with the genital glands. 
In the Scombridae the peritoneum is often dark coloured as in Rastrelliger 
and immature forms of Scomber probably owing to the body being broad, and 
abdominal wall thin, nearly vertical, and the light seems to transmit more or 
less ; but in adult forms of Scomber, Cybiidae, and Plecostei the peritoneum is 
little affected by the light, as the abdominal wall is thick and is turned 
obliquely downwards. Tlius the peritoneum remains nearly colourless in these 
groups. The peritoneum is developed round the visceral organs and envelops 
them, and the generative organs, rectum, etc. are suspended from the dorsal 
wall of the body-cavity by the peritoneum. The peritoneum is very thick at 
the posterior part of the body-cavity in Thunnus germo. 
AIR-BLADDER. 
The air-bladder is sometimes present and sometimes absent, and this is the 
case even among species of the same genus. The air-bladder is generally 
absent in those fishes living always near the surface of the sea. Thus it is 
entirely wanting in the fishes of the Katsuwonidae. It is, however, rather 
