COMPARATIVE STUDY OF SCOMBROID FISHES. 
363 
large masses of rete mirabilis of blood-vessels are found. In Parcithmms the 
external surface of the liver has a few short venules near the posterior margin ; 
but in Neothunnus no venules are found at the external surface. In these two 
genera the lobes of the liver are not deeply cut, and in the latter genus the 
right lobe is a little longer than the other lobes. In Euthynnus and Auxis 
(fig. 2) the right lobe of the liver is enormously elongated, almost reaching the 
anus, while the left lobe is often inconspicuous, being not separated by a distinct 
indentation from the middle lobe. In Auxis moreover dark and thick dendritic 
figures of the hepatic vein are clearly discernible on the external surface of the 
liver. 
The gall-bladder (figs. 1-3, 5, 6) is an enormously elongated sac, running 
along the intestine, on the inner side of the right lobe of the liver. The 
bladder becomes narrow at the anterior part and passes gradually to the cystic 
duct which is bent backward along the inner side of the middle lobe of the 
liver, and opens to the duodenum with a narrow duct, ductus choledochus. To 
the cystic duct three or more hepatic ducts open. These are more or less den- 
dritically branched in the liver. In the Scombridae the gall-bladder is elon¬ 
gated and receives some slender ducts (3 in Scomber jcvponicus). In the Ka- 
tsuwonidae the hepatic duct in the right lobe of the liver is very long, running 
the whole length of the lobe. The gall-bladder is greenish in colour, but it 
is sometimes purplish in a stale fish. 
The spleen (figs. 1-3, 5, 6) is a compact, elongated body, more or less 
compressed, and dark red or brownish in colour. It generally lies close to the 
junction between the duodenum and the small intestine. It is rather small in 
the Scombridae aud Cybiidae, but in the Thunnidae it is very well developed 
and is attached to the anterior part of the fold of the small intestine, occupy¬ 
ing the space enclosed by the duodenum, and the intestinal tract to the second 
bend. In the Katsuwonidae the spleen is again small and lies exterior to the 
intestine. In the genus Scirda the spleen is much separated from the liver. 
RESPIRATORY SYSTEM. 
In the so-called scombroid fishes the gill-openings are very wide, extending 
from the origin of the chin to the posterior ventral margin of the cranium, 
and the branchiostegal membranes not being united at the anterior end, remain 
