THE DIGESTIVE TRACT OF ELASMOBRANCHS. 5 
studied the mucous lining of the stomach of a great many species. In Cyprinids he 
was unable to find gastric glands. In other species, however, he found them abun- 
dant. As we shall see later, the lack of gastric glands is not peculiar to the Cypri- 
nidee, since many other fishes have no functional stomachs. 
Rathke (1841) found that the alimentary canal of Amphiorus (Branchiostoma) is 
composed of ciliated epithelium without glands, and Johannes Miiller (1843), in his 
work on the myxinoids, arrived at the same results. By these investigators the 
simplicity and uniformity of the mucous lining of the alimentary canal in the lower 
fishes was fully established. 
Vogt (1845) proved the existence of two kinds of cells in the stomach of the 
common trout, Salmo fario, i. e., cells of cylindrical epithelium, covering the 
surface, and round cells in the crypts. Vogt, however, did not recognize these 
crypts as gastric glands. Leydig (1852), on the other hand, clearly recognized the 
gastric glands in Sguatina angelus and in Torpedo galvani, since he writes of the 
small round cells, containing highly granular protoplasm, as granular cells. In 1853 
Leydig found such glands in the sturgeon, Acipenser nasus, but could not find 
them in the stomach of the loach, Cobitis fossilis. In a still later paper Leydig 
(1857) referred to these glands as “‘labdriisen,” thus signifying that they were like 
the gastric glands of higher vertebrates. 
Since 1857 much work has been done on the histology of the alimentary canal of 
fishes, and especially on the histology of the stomach. Perhaps the best reviews of 
previous work are presented by Edinger (1877), Richet (1878), and Yung (1899). To 
the works of these authors I am greatly indebted. 
One of the earliest workers on the glands of the stomach of fishes was Valatour 
(1861), who noticed the presence of gastric glands in various species and confirmed 
Bischoff's work in that he could find no functional stomach in Cyprinide. From 
1861 to 1870 much advance was made in histological technic, and in 1870 Heiden- 
hain discovered two kinds of granular cells in the mammalian stomach, and Rollet 
the same year confirmed his discoyery. These cells are now known as chief and 
parietal cells. In fishes, on the other hand, Edinger (1877) could not find the two 
kinds of gastric cells distinguished by Heidenhain and Rollet in the mammalian 
stomachs. Of Edinger’s work we may speak in detail. 
Edinger (1877) made a detailed histological study of the entire digestive tract 
of fishes. According to kis investigations, the stomachic crypts are only partly lined 
with gastric glands, for in the pylorus the crypts are functional merely as mucous 
glands. The pyloric appendages are simply evaginations of the intestinal wall and 
present the same structure as the part from which they arise. Properly speaking, no 
glands exist in the middle intestine, and the mucous cells are the only secretory part. 
The other epithelial cells are merely absorptive in function. Finally Edinger paid 
much attention to the question as to whether or not chief and parietal cells exist in 
fishes. He concluded that there is only one kind of cell in the gastric glands—a cell 
which is homologous to neither of these cells. 
Edinger’s conclusion has been generally accepted, althougn several authors have 
noted differences in the cells of the gastric crypts. Thus Cajetan (1883) ealled atten- 
tion in the case of Cobitis burbatula to the fact that the cells of the stomach differ 
with respect to the dimensions of their granules and their staining reaction to osmic 
