THE DIGESTIVE TRACT OF ELASMOBRANCHS. 11 
stomach, which is always reddish in color, especially noticeable when the stomach 
is full of food. In the beginning of the esophagus the epithelium is similar to that 
of the buccal cavity, but it is gradually replaced by an epithelium consisting of 
ciliated cylindrical cells and goblet cells. 
MUCOUS MEMBRANE OF THE STOMACHIC SAC, 
The mucous membrane of the stomach has a reticulated appearance, due to 
numerous folds. Some of these folds are continuations of the longitudinal folds of 
the esophagus, while others are transverse and oblique. In the pyloric tube the 
folds are extremely fine. Histologically, the mucous membrane of the stomachic sac 
differs from that of the esophagus by the absence of cilia and of goblet cells, and 
by the presence of true peptic glands. 
The epithelium of the stomachic sac is of two kinds, superficial and glandular. 
The first is composed of a single layer of prismatic or pyramidal cells with oval 
nuclei. In these, two portions may be distinguished—one, finely granular, which 
incloses the nucleus and occupies four-fifths of the length of the cells; and another, 
the superficial part or the part nearest the cavity of the stomach, composed of a 
highly refractive, nonstaining, transparent substance. These two portions, as 
Yung (1899) has pointed out in his work on Scyl//wm canieula, corresponded to what 
Oppel (1897) called the protoplasmic portion and the upper portion. The refractive 
superficial portion of these cells has been called *‘ Pfroph” or ‘* plug” by Bieder- 
mann (1875), and is considered by Oppel as a substance comparable to mucus. The 
superficial epithelium, which is rather uniform in character, covers all the folds of 
the mucous membrane and the superficial portions of the glandular tubes. 
The glandular tubes begin in the cardiac end of the stomach and extend to the 
pylorus, being most plentiful in the middle of the stomachic sac. Each gland is a 
eylindrical tube, with the canal narrow in the upper part but wider toward the bot- 
tom. The tubes in the middle of the stomach are longer than those of the cardiae 
end or the pyloric end of the sac. In every case they are separated from each 
other by a fine layer of connective tissue. The epithelium of the neck of *the peptic 
erypts consists of cylindrical cells, like those of the superficial epithelium, which 
become little by little shorter and thicker. They are distinguishable from the 
superficial layer, however, by the absence of the mucous plug, and by the presence 
of a large round nucleus. They differ from the neighboring peptic cells by their 
clearer contour, smaller size, and the smaller amount of granulation. The body of 
the gland is occupied by cells which are irregularly polygonal in shape, highly granu- 
lar, and closely packed together. These cells are all of one kind, and can not be 
differentiated into chief and parietal cells, such as Heidenhain and Rollet have found 
in the mammalian stomach. 
PYLORIC TUBE. 
In the long narrow pyloric tube we find crypts and the same superficial epithe- 
lium as in the stomachice sac. The crypts, however, are short and the polygonal 
peptic cells are absent. 
INTESTINE. 
The intestine of elasmobranchs may be divided into two porti au small 
intestine or duodenum, and a large intestine. The former is short, varying from one- 
B. B. F. 1907—2 
