354 KAiUKlCAI KISHDtOUYE: 



Trat in the Cybiiclae the cavity is more or less separated from the vertebral 

 cokimn, fr-om the development of tho Liemal processes in many precaudal 

 vertebrae. In the the Plecostei the coelomic cavity is low and nan-ow, as tlie 

 haemal process of precaudal vertebrae is mnch better developed than in the 

 Cybiiclae. The height of the cavity is less than its breadth, and its roof is 

 flat or convex, tliatched with a broad proximal portion of ribs, and protected 

 by the peritonemn, composed of thick bimdles 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 veuti-al 

 median line of the cavity, hoi-e too, their ends are interwoven. Generally 

 speaking the visceral cavity of the scombroid fishes does not extend t<i the 

 caudal portion, though some posterior ribs push their way into the lat«ryl 

 muscle, beyond the ^leritoneum, and He on each side of the interhaemals. Thus 

 the length of the alxlominal cavity may approximately be known by measuring 

 the distance of the anus from tlie giU-slit. In the genus Avxis, however, the 

 genital gland extends beyond the origin of tlie anal, and grasps the inter- 

 haemals of the fin fr-om both sides. Thus the abdominal cavity is aJso extended 

 backward beyond the anus with the genital glands. 



In the Scombridae the peritoneum is often dai'k coloured as in BastrelUger 

 and immatm-e forms of Scomber probably o^ving to the body being broad, and 

 alxlominal wall tliin, nearly vertical, and the hght seems to transmit more or 

 less; but in adiüt forms of Scomher, Cybüdae, and Plecostei the pei-itoneum is 

 little afiected by the hght, as the abdominal wall is thick and is turned 

 obliquely downwards. Thus the peritoneum remains ueai'ly colom-less in these 

 gi-oups. The peritoneum is developed roimd the visceral organs and envelops 

 them, and the generative organs, rectmn, etc. s\xe suspendetl from the dorsal 

 wall of the body-cavity by the peritoneum. Tlie jieritoneum is very thick at 

 the posterior part of the body-cavity in Tkwinus germo. 



AIR-BLADDER. 



Tlio air-bladder is sometimes present and sometimes absent, and this is the 

 case even among species of the same genus. Tlie air-bladder is generally 

 absent in those fishes Hviug always neiur the surface of the sea. Thus it is 

 entirely wanting in the fishes of the Katsuwonidjui. It is, liowever, ratlier 



