Abstract
APPENDIX F of the Report of the Scottish Fishery Board contains a series of valuable papers with accu rate and well executed plates. Dr. Stirling gives a pre liminary report on “The Chemistry and Histology of the Digestive Organs of Fishes.” The first part gives the results of chemical investigations of the digestive processes in the herring, cod, haddock, and skate. The second part deals exclusively with the intestinal tract of the herring. The muscular coat of the oesophagus consists of striped muscular fibres arranged more or less regularly at the upper part, but disposed circularly in several layers at the lower. The mucous membrane of the œsophagus has longitudinal folds, and is lined with cylindrical epithelium interspersed with numerous goblet cells. The œsophageal glands are simple tubular glands, with, at first, a very short secreting portion. The glands in the “cardiac sac,” or “crop,” are, like those of the œsophagus, branched tubular glands lined in their upper part by tall columnar epithelium, and in their secretory parts by a single layer of cubical cells, like the “outer” cells of the fundus in mammals. The gland tubes become shorter towards the lower part of the cardiac sac, and they are absent in the pneumatic duct, which is lined by a single layer of columnar epithelium, and divided into two compartments by folds of the mucous membrane. Dr. Stirling has found that the organ which has been hitherto known as the “crop” in the herring, is something more than a mere receptacle, and corresponds in structure and function to the cardiac portion of the stomach of higher vertebrates. There is a striking resem blance between the cells lining the secretory portion of the gland tubes and the “outer cells” in the mammalian stomach, the point of difference being that the tubes are lined by a single continuous layer of these cells. There are apparently no internal layers of cells comparable to the inner cells of mammals, and, as might be perhaps expected, the glands are simpler than those of the mammals, and without that differentiation of tissue which is brought about by specialisation of function. One cell may sub serve two functions, and, from an evolutionist's point of view, the secretion of an acid and the formation of a ferment have not as yet in the fishes been relegated to two distinct sets of cells. The pyloric sac or stomach is that short tubular organ with thick muscular walls, and resembling a gizzard, which opens out of the crop and is continued into the in testine. The surface of the mucous membrane consists of irregular depressions, which are deeper than those of the cardiac sac and may be regarded as crypts. The pyloric sac is always lined by a very thick coating of mucus, which not only lies on the surface, but dips down into the pyloric crypts. The surface of the pyloric sac and the glands or crypts are lined throughout with a single layer of tall, narrow, columnar epithelium, having the same character as that which lines the gland ducts and the surface of the cardiac sac. There is no muscularis mucosae. The circular muscular coat is very thick, while the longitudinal is thin. Structurally the pyloric sac is comparable to the pyloric end of the mammalian stomach. Plates i. and ii. give series of figures illustrating various points in the anatomy of the intestinal part of the herring.
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Scottish Fishery Researches . Nature 30, 572–573 (1884). https://doi.org/10.1038/030572a0
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DOI: https://doi.org/10.1038/030572a0