88 
BUIyl^ETlN OE THE BUREAU OF FISHERIES 
intestinal coats. 
The coats of the intestinal tube are not so numerous as in the stomach. Certain 
parts present in the latter organ are not present in the intestinal tract, either in the 
intestine proper or in the pyloric caeca. Those structural coats that are present in the 
intestine are the following, beginning with the mucous membrane; 
I. Mucosa. 
1. Epithelial coat. 
2. Tunica propria. 
3. Stratum compactum. 
4. Stratum granulosum. 
II. Muscularis. 
1. Muscularis circularis. 
2. Muscularis longitudinal is. 
III. Serosa. 
histology of The mucosa. 
Epithelial coat . — The epithelial coat of the intestinal mucosa is very simple as 
to structure, but rather complex as to its folding. A section at right angles through 
this coat will always show a single layer of columnar epithelial cells. I have been 
unable to show any differentiation in the structure of these cells in the different regions 
of the coat. The foldings of the mucous epithelium, however, are so complicated that 
it is difficult to secure right-angled sections through any great extent in any single 
section. In a cross section of the middle portion of the intestine which is uncompli- 
cated by the origin of pyloric coeca, it will be noted that the mucosa is thrown into 
relatively complex longitudinal folds (figure 5). Occasionally in a widely distended 
intestine these folds are somewhat smoothed out, so that the arrangement seems less 
complex. If, however, the intestine be sharply contracted, then there are not only 
general longitudinal folds but many smaller collateral folds. Edinger “ in one of his 
plates presents a series of figures to show the character of the folding of the mucosa 
in fishes. The type of folding that he figures holds for the intestine of the salmon. 
In another place ^ I have given a brief description of this folding as it appears in the 
pyloric caeca. There, however, the mucosa is more simple in its arrangement than 
in the intestine. 
In a transverse section through a longitudinal fold in the intestinal mucosa the 
fold or ridge itself will have secondary pits or grooves on its lateral extent. Very often 
it happens that the section will present the appearance of definite tubes, or be through 
what looks like simple tubular glands, or sections of wide oval loops of epithelium will 
be shown. The tubelike structures do, indeed, suggest definite intestinal glands in 
the mucosa, but there is absolutely no histological differentiation between the cells 
of these narrow pitlike folds and the cells of the free epithelial surface. Although 
the folding of the epithelium is rather complicated one must accept the fact that the 
complexity of folding is not accompanied by histological differentiation of structure. 
o Edinger, L.: Ueber die Schleimhaut des Fischdannes, nebst Bemerkungen zur Phylogenese der Driiseu dcs Darmrohres. 
Archiv fiir mikroskopishe Anatomie, bd. xm, 1877, p. 651. 
& Greene, Chas. W.: “The absorption of fats by the alimentary tract with special reference to the function of the pyloric caeca 
in the king salmon, Oncorhynchus tschawytscha/* Transactions of the American Fisheries Society, 1911, p. 261. 
