376 KAMAKICHI laSHINOUYE: 



the blue-finned tuua from San Pedro, Cal., I foimd the axial margin of the 

 cutaneous vein partly covered by the abaxial margin of the accompanying 

 artery. In Eidhynnus (all kno-ma species iuclusive), however, the cutaneous 

 artery Ues on the abaxial side of the accompanying vein, and the axiiil margin 

 of the cutaneous artery is partly covered by the abaxial margia of the 

 accompanying vein (fig. 26). The distribution of smaller canals on the wall 

 of the cutaneous arteries is variable in difi'ereut species, and so far as I have 

 examined, there are no two Japanese sjaecies of timnies which luive the aiierioles 

 distributed ia the same way (figs. 20-24). 



In Thunnus germo arterioles are distributed on the external axial side of 

 the artery hi two or more rows, and they run axially. In Thunnus orienicdis 

 arterioles are found on the interruil side in one row, in Parcdhunnus mehachi 

 iu two rows, internal and external, in Ntothunnus mcwropterm in one row or 

 two indistinctly aitenaate rows on the side near the lateral median line of the 

 body, and iu Neothuimus rarus in one or two alternate rows at the middle of 

 the abaxial side. In the Katsuwonidae, the cntaaieous artery of the epaxial 

 side would be homologous to both the epaxial and hypaxial branches of the 

 cutiuieous artery of the Thunnidae. The liypaxiiil cutaneous artery of the 

 Katsuwonidae is remarkably short and slender, it generally origiuates iu front 

 of the epaxial artery, and takes a forward direction, and after passing through 

 the kidney turns backward, it is situated in a more ventral position than the 

 hypaxial branch of the cutaneous artery of the Thimnidae. Iu Kaisuivcnius the 

 epaxial and hypaxial arteries are nearly equal and origimxte fi'om a common 

 lateral branch of the dorsal aorta, in the hiud part of the st^ment of the sixth 

 vertebra, just behind the pharyngeal muscle. The common lateral branch of 

 the dorsal aorta ia very short, horizontjil. It is divided iu the kidney into 

 two canals or rather it is united to a gently curved caual, two Umbs of 

 which are turned backward. The epaxial hmb passes beneath the fiist rib 

 and then between the intermuscular" bones of the second and third vortebnie, 

 while the hypaxial hmb passes over the first rib. In Katmioonus the cutaneous 

 artei'y is obviously narrower in cahbre than the dorstil aorta, and the epaxial 

 and hypaxial branches are much more sepirated from the kteral methan line 

 thiin in timnies. The arterioles from these branches are given off at the sm-fiiiCe 

 of the body, between myotomes on both sides of each branch, dorsal and 



