COMPARATIVE STUDY OF SCOMBROID FISHES. 371 



lateral median line (if the bfxly, ruauiug to tlio doojx'r part of tl«; bodj 

 lietween the myotomes of the fom-tli and fifth vertebrtie. Tlie cliit'f cutanooua 

 segmental veins are united to the ejiaxial cutiineous vein, and sheets of 

 Tascular plexus smToimding the daik nni portion of tho lateral muscle are 

 connected witli tlit- win. Tli(> hypnxial cutaneous vein is remarkably short, 

 slender, and zigzag in its course, disappearing from the surfaoe of the body 

 just lx)hind the \x>stclavicle mid liefoi-e the myotome of the first vertebra. In 

 the Katsuwouidiie the hyiiaxial cutaaeous vein always passes before and above 

 tlie fii-st rib. The posterior ciuxhual vein leaves the hjvemal canal from tho 

 foui-teeuth vei-tebra or a still more backward pjsition. Anterior to that point 

 the posterior cardinal vein is more or less separated from the dorsal aortii, 

 receiving several short but comparatively large veins at both sides of the 

 dorsal aorta, and these veins are formed fi'om parallel venules of the A'ascular 

 plexus in tlie haemal canal or " km'ochiai " in Japanese. At the same point 

 an inferior posterior branch joins the postei'ior cardinal vein. Tlie branch is a 

 slendei" renal vein as in NeotMoinus. Tho cardinal vein and the doi'sal aorta 

 too are situated close to the lower side of the haemal canal, sending a thick 

 ixxl of vascular plexus above, which fills up the broad canal. Tho kurochiai 

 api^ears fi."om the segment of the fifth vertebra in Katsuioonus, from that of the 

 sixth vertebra in Euthijrmm yaito, from tbit of the ninth in Neothunnus, and 

 tenth or twelfth in Auxis. Li the latter genus the epasial cutaneous vein 

 passes between the two accessory cones of the lateral muscle (fig. 2). 



ITie visceral venous system of the Plecostai consists of some hepatic portal 

 veins, hepatic veins, and genital veins. The chief chfierence fi'om the CybiidiW) 

 and Scombridae lies in tlie genital veins, wliich chrectly join the Cuvierijin 

 ducts. In the Tliimui(Lae the hepatic pjrtal veins are more or less divided 

 into plexuses or parallel venules before entering the liver. The plexus is most 

 remarkably developed in Thunnus. In tliis genus the vejiules ai'e interhiced 

 with arteiioles of the ooehac artery. Each plexus is as large as a fist, and is 

 more or less conical. In smother genus, Parathunnns, only venules are foimd in 

 the plexus, conserpieutly the plexus is thin, elongated, and in tho genus Neothunmm 

 the jJexus is not found at all, but instead of a single ti-iuik, the liepitic 

 poiial veins ai'e compjsal of several psu'allol venules. Concomitantly with the 

 development of the ixjculiar plexus on tlie internal side of the liver, the 



