COMPARATIVE STUDY OF SCOMBROID FISHES. 
359 
with the duodenum. In the Plecostei the pylorus is rounded or more or less 
ovoidal, being thicker at the proximal portion, and more or less twisted to 
the right-hand side at the posterior end. The duodenum is separated from the 
pylorus by a well marked constriction, and suddenly dilates, hence it is more 
or less sac-shaped. It is thin walled, widest just behind the pylorus, overlapping 
the latter a little and becoming gradually narrow. It is curved forward, touc hing 
the dorsal posterior surface of the liver, and is bent dors* lward, then backward, 
and lastly bending to the right-hand side, passes to the intestine. In more or 
less tainted fish the duodenum is the first to dissolve, probably by its own en¬ 
zymes, 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 enters at the 
anterior side of the duodenum, just near the pylorus, while the former generally 
open at the posterior side with many apertures, distributed in one or several 
rows. The pyloric coeca are generally yellowish in colour. 
Longitudinal folds of the stomach are mostly about 20 in the Cybiidae, but 
in the Thunnidae there are usually 30-40, but in the Katsuwonidae they de¬ 
crease in number again, to about 20 in Katsuwonus, 12 in Euthynnns , and 
nearly indistinct in Anxis. 
Pyloric coeca. In the Scombridae (fig. 1) the pyloric coeca are coarse, 
numerous, and each coecum communicates directly with the duodenum {Scomber), 
or a few or several coeca coalesce at the root and open by a common orifice 
( Rastrelliger ). They are crowded in a long and more or less triangular tract on 
the posterior or ventral side of the duodenum. Those coeca near the pylorus 
are long, and their length gradually diminishes in proportion to the distance they 
are from it. These numerous coeca are connected by loose connective tissue 
traversing them. 
In the Cybiidae (fig. 6) and Plecostei (figs. 3, 5) the pyloric coeca are re¬ 
markably well developed and assume 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 duodenum, but to its tubular outgrowths of varying length. These tubules 
are dendritically branched, have a rather thin but tough wall, and some longi¬ 
tudinal grooves inside. They are more or less capable of distention. Each 
branch of the pyloric tubules -with tufts of coeca is enclosed by a membrane of 
