+ BULLETIN OF THE BUREAU OF FISHERIES. 
which is usually furnished with a valve at its posterior end. The digestive tract 
may be straight, U-shaped, or Y-shaped—straight in Branchiostoma and the cyclo- 
stomes; syphonal or U-shaped in the elasmobranchs and in some teleosts, where the 
stomach presents the form of a bent tube, of which one half is the cardiac and the 
other the pyloric portion; cecal or Y-shaped in most teleosts, where the cardiac 
division is a long, descending blind sac, with the cardiac and pyloric openings of the 
stomach lying close together. In most cases the pyloric tube is long and slender. 
In many fishes, especially among ganoids and teleosts, a variable number of 
blind tubes open inta the intestine immediately posterior to the pylorus. These 
tubes are termed the pyloric ceca and are often filled with the same material as is 
the intestine. When present in large numbers, the appendages often coalesce into a 
common duct. In the eyclostomes and dipnoans no pyloric appendages exist, and in 
the elasmobranchs pyloric cxeca have been’ found by Turner (1878) only in the 
Greenland shark, Lemargus borealis, and by Gegenbauer (1892) in certain skates. 
The duodenum receives the hepatic and the pancreatic secretions, and also the 
secretion of the pyloric appendages. 
The intestine varies much in length, and in many fishes the absorbing surface is 
increased by folds of the mucous membrane, which wind spirally or are arranged in 
parallel lamelle. These spiral valves are found in cyclostomes, selachians, ganoids, 
and dipnoans. In short, the digestive tract in fishes varies greatly, from a simple 
condition to a complex one, with valves, folds, and appendages. 
The pancreas is the most constant of all digestive glands in vertebrates. In the 
lower fishes it occurs as a compact mass, while in the teleosts it is, as a rule, diffused 
and distributed about the pyloric ceca, hepatic duct, and in the liver. The presence 
of the pancreas in bony fishes in a widely diffused state was demonstrated by Legoius 
(1873). In the elasmobranchs the pancreas is comparatively large, and pinkish in 
color. It empties by a single duct into the duodenum. 
Crcal appendages at the end of the intestinal canal are of exceedingly rare 
occurrence in fishes. In the elasmobranchs, however, an appendage, the so-called 
rectal gland, exists near the end of the intestine. This gland varies from half an 
inch in length in the skate to three or four inches in the big sharks. According to 
Wiedersheim (1905, p. 422), cloacal appendages exist in the dipnoans and traces of a 
blind intestine may be found in certain teleosts, while in the Holocephaii the place 
of the rectal gland is taken by glandular tissue within the walls of the rectum. 
For a more detailed account of the gross anatomy of fishes the reader is 
referred to Home (1814), who described the intestines of thirty species, and to 
Rathke (1824), who described fifty-six species. General works on the intestinal canal 
of fishes are Siebold and Stannius (1854), Milne-Edwards (1860), Giinther (1880), 
Oppel (1896, 1897, 1900, 1904), and Wiedersheim (1905). 
HISTOLOGY. 
Though Nehemiah Grew (Gamgee, 1893) made mention, in 1676, of a glandular 
secretion in the stomach of the horse, it was not until 1836 that the gastric glands 
were actually discovered. In this year Boyd (1836) discovered gastric glands in 
mammals and noticed their presence in some fishes. Following Boyd, Bischoff 
(1838), one of the earliest workers on the histology of the alimentary canal in fishes, 
