COMPARATIVE STUDY OF SCOMBROID FISHES. 
367 
same journal, Yol II (46). 
Besides the peculiar cutaneous system and vascular plexuses on the inner 
side of the liver described by Eschricht and Müller there is another peculiar 
plexus in the haemal canal of the vertebral column in Neothunnus and Iva- 
tsuwonidae. In these fishes the vascular plexuses on the inner side of the 
liver and fine hepatic veins on the outer side of the liver are wanting. There¬ 
fore these hepatic plexuses seem to be the alternative of the plexuses in the 
haemal canal. Both the hepatic plexuses and the plexuses in the haemal canal 
consist of blood-vessels entirely filled with blood-corpuscles. 
In the Plecostei the caudal peduncle is very slender and full of strong 
tendons, thus there is little space for the sure circulation of blood, and here 
blood-vessels find a safe passage in the substance of the vertebrae themselves. 
The higher temperature of the body than the surrounding water, and 
consequently great activity of fishes of the Plecostei is undoubtedly due to the 
peculiar circulatory systems above described. 
Yenous system. In the Scombridae (fig. 1) the chief vertebral venous 
system consists of the jugular veins, Cuvierian ducts, posterior cardinal vein, 
lateral vein, and segmental veins. The visceral system consists of the hepatic 
veins, hepatic portal veins, and the genital veins from the gonads. The genital 
veins unite with the posterior cardinal vein separately. The posterior cardinal 
vein lies below the dorsal aorta and communicates with the Cuvierian duct of . 
the right side. The segmental veins carry venous blood along the neural and 
haemal processes and intermuscular bones, generally in every other myotome, 
alternating with segmental arteries. The venous blood from the surface of the 
body is collected in these segmental veins, but chiefly in those running to the 
inner surface of the wedge-shaped superficial reddish muscle and then along 
intermuscular bones. These segmental veins are short and small. The venous 
blood in the lateral wall of the abdominal cavity is chiefly collected in the 
segmental veins along the peritoneum and pour to the posterior cardinal vein 
at the root of the pleural ribs, and partly to the lateral veins running along 
the ventral median line, collecting some inferior segmental veins in the antero¬ 
inferior part of the lateral body wall. The Cuvierian ducts are large vertical 
ducts, running along the sides of the oesophagus, behind the pericardo-peritoneal 
septum and join the sinus venosus. 
