CüitPARATIVE STUDY OF SCOMBROID FISHES, 367 



same jourual, Vol II (46). 



Besides the peciiliar cutaneous system and vascular plexuses ou the inner 

 side of the liver descriljed by Eschuicht and MÜLLER there is another peculiar 

 plexus in tlie haemal cannl of the vertebral column in Neothunnus and Ka- 

 tsuwonidao. In those fishes the vascular plexuses on the inner side of the 

 liver and line hepatic veins ou the outer side of the hver are wanting. There- 

 fore these he^jatic 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 caudiil i«dunclo 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 jiassage in the substance of the vertebrae themselves. 



The higher temperatm'e of the body than the suiToundiug water, and 

 consequently great activit}' of fishes of the Plecostei is undoubtedly due to the 

 peculiai" circulatory systems above described. 



^'enous 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 ixtsterior cardinal vein separately. The ixeterior cardinal 

 vein lies below the dorsal aoiia and communicates with the Cuvierian duet of 

 the right side. The segmental veins carry venoas blood along the uem-al and 

 haemal processes and intermuscular bones, generally in every other myotome, 

 alternating with segmental ai-teries. 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 iwm- to the posterior cardinal vein 

 at the root of the pleural ribs, and partly to the lateral veins running along 

 the venti'al 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-peritoueal 

 septum and join the sinus veuasus. 



