COMPARATIVE STUDY OF SCOMBBOID FISHEa- 359 



with tbo (iHodimum. lu the Plucostei tbo pylorus is roiindccl or more or less 

 ovoidal, being thicker at the proximal portion, and more or loss twisted to 

 the right-hand side at the posterior end. The duodenum is separated from the 

 pylorus by a well marked constriction, and suddenly dOatcs, hence it is more 

 or less sac-shaped. It is thin walled, widest just behind the pylorus, overlapping 

 the latter a httle and becoming gradually naiTow. It is curved forward, touching 

 the dorsi J posterior surface of the liver, and is bent dors« Iward, then b;ickward, 

 and histh- bending to the right-hand side, passes to the intestine. In more or 

 less tainted fish the duodenum is the firet to dissolve, probably by its own cn- 

 zjTues, i. e. by the action of autolysis. To this portion of the intestine the pylo- 

 ric coeca and cystic duct open their apertures. The latter duct entere at the 

 anterior side of the duodenum, just near the pylorus, wlule the former generally 

 open at the postwior side with noany apoi-tm'es, distiibuted in one or several 

 rows. The pyloric coeca are generally yellowish in colom*. 



Longitudinal folds of the stonuich are mostly about 20 in the Cybiidae, but 

 in the Thiumidixe there are usually 30-40, but in the Katsuwonidae they de- 

 crease in number again, to alx)ut 20 in Katsincaiius, 12 in Euthynnm, and 

 neai'ly inthstinct in ^Ivxis. ^ 



Pyloric coeca. In the Scombridae (fig. 1) the pyloric coeca are coarse, 

 numei'ous, and each coecum communicates dii'ectly with the duodenum (Scomber), 

 or a few or several coeca coalesce at the root and open by a common orifice 

 {Rastrellnjer). They are ci'owdod in a long and more or less trianguhu" tract on 

 the postei'ior or ventral side of the duodenum. Those coeca near the pylorus 

 ai"e long, and their length gi-adually diminishes in proportion to the distance they 

 ai'e fi'om it. Tliese numerous coeca ai"e connected by loose connective tissue 

 ti'aversing them. 



In the Cybiidae (fig. 6) and Plecostei (figs. 3, 5) the pyloric coeca are re- 

 markably well developed and assmne a conspicuous size as a mass. The size 

 of each coecum, however, becomes small as the development of the pyloric coeca 

 as an organ advances. In these groups of fish the coeca do not open directly 

 to the duodejimn, but to its tubuhu- outgrowths of vtu'ying length. These tubules 

 are denthiticaUy biimched, have a rather tliiu but tough wall, and same longi- 

 tudmal gi'ooves inside. They are more or less capable of distention. Each 

 branch of the pyloric tubules with tufts of coeca is enclosed by a membnine of 



