COMPARATIVE STUDY OF SCOMBROID FISHES. 
379 
RENAL ORGANS. 
The kidneys are well developed in the Scombridae and Cybiidae. They 
are paired, very thick at the sides of the pharyngeal muscles, but behind these 
muscles they are blended together and become gradually narrow towards the 
caudal portion. In Sarda orientalis the kidneys are united before the pharyn¬ 
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 membrane 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 seen scattered all over them. These are due to the 
pigment cells accumulated in glomerules. In the Plecostei the kidneys are 
generally concentrated in the pectoral region. This is especially the case in 
primitive forms of the order, for instance, in Thunnus germo and Th. orientalis 
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-like organ enters 
the haemal canal and runs 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 dorsal wall of 
the abdominal cavity. In the Katsuwonidae the oblong space for the passage 
of the pharyngeal muscles is divided by a median longitudinal bridge of kidneys. 
The seemingly renal organs in the haemal canal are detached from the main 
body in Katsuwonus. In Auxis the renal organ is not found in the haemal 
canal. It is not developed in the cephalic region, and its posterior part is divi- 
« 
ded into two long slender bodies, running on both 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 median 
duct, before opening to the urinary bladder. In the Thunnidae they are united 
to a long median duct, but they are nearly separate again in the Katsuwonidae. 
In Thunnus germo two meters meet nearly in a transverse line, perpendicular 
to the median united duct, and at the middle of the former there is a short 
