COlirARATIVE STl'DY OF SrOMBKOID FBHES. 379 



RENAL OIlG.\NS. 



Tlie kidneys are well developed in the Scombridae and Cybiidae. Tlicy 

 me paiied, very thick at the sides of the plmryngeal nnisclos, but behind these 

 muscles they are blended t )gcther and bocoino gradually narrow towards the 

 caudal portion. In Sarcla orlcnlalis tli<! kidneys are united Ijefore the phiirj'ii- 

 geal muscles. The organs reach the otic region of the cranium, then run along 

 the ventral side of the vertebral column, between the base of ribs, and lie above 

 the peritoneal membi-ane of the air-bladder, when it is present. The organs 

 often reach the anus posteriorly. They never enter the haemal canal. The 

 kidneys are reddish in colour, which become paler in preserved specimens and 

 minute black spots may be seeu scattered all over them. Tliese are due to the 

 pigment cells aocumuLitt'd iu glomerules. In the Plecostei the kidneys are 

 generally conccutrnted in the ptctoral region. This is especially the case in 

 primitive forms of the order, for insta,nce, iu Tliunnus germo and Hi. orimtalis 

 the kidneys are more or less ring-shaped, as the organ of one side is connected 

 to the organ of the other side at the anterior and posterior sides of the pharyn- 

 geal muscles. In these forms of tunnies a slender kidney-Uke organ enters 

 the haemal canal and rims more or less posteriorly, just below the vertebral 

 column. The organ is thickened at the root of each haemal arch. In other 

 forms of tunnies the kidneys are elongated backward along the doi-sal wall of 

 the abdominal cavity. In the Katsuwonidao the oblong spice for the passage 

 of the pharyngeal muscles is divided by a median longitudinal biidgc of kidneys. 

 The seemingly renal organs in the haemal canal are detached from the main 

 body in Katsutvonus. In Aiixis the renal organ is not found iu the haemal 

 canal. It is not developed in the cephahc region, and its posterior part is divi- 

 ded into two long slender bodies, nmuing on lx)th sides of the posterior car- 

 dinal vein. 



In the Scombridae the ureters are nearly separate from each other, in the 

 Cybiidae they are separate for the most part, but are united to a short mediin 

 duct, befoi-e openiug to tlie urinary bladder. Iu the Thunnidae they are imited 

 to a long median duct, but they are nearly separate again in the Katsuwonida«. 

 In Tliunnus germo two m-eters meet nearly in a transverse line, perpendicular 

 to the median imited duct, and at the middle of the former there is a short 



