358 K-iMAKICHI KISHINOUYE: 



rakers, and in the genus Kaisuwonm the gill-rakers are better developed than 

 in the genns 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 Uttle larger than others. Thus teeth on the lower 

 pharyngeals and the hypobranchial segment of the foui'th 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 giU-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 

 waUed, conical sac, suspended from the roof of the coelomic cavity of the ]^X!ritoneum, 

 and weak longitudinal folds (about 16 in Scomler japonicus) are found near the 

 two oiifices, 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. tm-ned anteriorly. It opens into the duodeniun with a crescent-shaped 

 orifice, as its posterior waU 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 turned posteriorly. The wall 

 of the stomach is thick, tough, and rich in deep, longitudinal f jlds, 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 lejiving 

 the chondrous substance behind. The gelatinous tissue or tunicine of pteropods, 

 tiuiicates, &c., jaws, pens, and lenses of cuttle-fish are scarcely (^hanged in the 

 .stomach. The stomach of tunnies is very loosely covered outside with the thick 

 peritoneum, and the blood-vessels to the stomach he mider tlie membrane. 



The pylorus is more muscular than the sac-portion, and genei-ally 

 rather short. It nms to the left side of the stomach. In the Scombridiie and 

 in the majority of the remaining teleosts the pylorus is ascending. In the 

 Cybiidae the pylonis is slender, variable in length, and is more or less dilated 

 near the distal end, foinaing a special diverticulum, just before the boimdary 



