358 
KAM AKICHI KISHINOU YE : 
rakers, and in the genns Katsuwonus the gill-rakers are better developed than 
in the genus Thunnus. The inner or axial side of gill-rakers and also calcare¬ 
ous grains on branchial bones are covered with villous teeth. Teeth near the 
oesophagus are generally a little larger than others. Thus teeth on the lower 
pharyngeals and the hypobranchial segment of the fourth branchial arch are 
larger than those on other branchial bones. 
In the Katsuwonidae the second, third, and fourth gill-arches carry numer¬ 
ous, thin, elongated gill-rakers, also on the posterior side. In Katsuwonus, more¬ 
over, the inner margin of the gill-rakers on the anterior margin undulates. 
Stomach (figs. 3, 5, 6). In the Scombridae the stomach is a rather thin 
walled, conical sac, suspended from the roof of the coelomic cavity of the peritoneum, 
and weak longitudinal folds (about 16 in Scomber japonicus) are foimd near the 
two orifices, pyloric and cardiac. The cardiac orifice is more or less constricted. 
The pyloric orifice, situated about midway of the stomach is long and ascending, 
i. e. turned anteriorly. It opens into the duodenum with a crescent-shaped 
orifice, as its posterior wall is enormously thickened. In the Cybiidae and 
Plecostei the stomach is a very long conical sac, the posterior end of which al¬ 
most reaches the anus. The pylorus, situated quite near the oesophagus, is on 
the left side of the stomach, and is more or less tinned posteriorly. The wall 
of the stomach is thick, tough, and rich in deep, longitudinal folds, some of 
which run into the pylorus. The food is chiefly digested in the sac-portion, 
where the soft parts are almost entirely dissolved and the framework of the hard 
skeleton is also broken to pieces. The digestive fluid of the stomach is acid in 
reaction, very powerful, soon dissolving the skin of fish or cuttle-fish, then muscles, 
and lastly bones. The calcareous portions of the skeleton are dissolved leaving 
the chondrous substance behind. The gelatinous tissue or tunicine of pteropods, 
tunicates, &c., jaws, pens, and lenses of cuttle-fish are scarcely changed in the 
stomach. The stomach of tunnies is very loosely covered outside with the thick 
peritoneum, and the blood-vessels to the stomach he under the membrane. 
The pylorus is more muscular than the sac-portion, and generally 
rather short. It runs to the left side of the stomach. In the Scombridae and 
in the majority of the remaining teleosts the pylorus is ascending. In the 
Cybiidae the pylorus is slender, variable in length, and is more or less dilated 
near the distal end, forming a special diverticulum, just before the boundary 
