The Physiology of the Digestive Tract of Elasmobraxchs
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چکیده
S IXTEEX per cent of the dogfish taken at the laboratory of the Bureau of Fisheries, Woods Hole, Mass., during the summer of 1904, were found to contain lobsters ; 34.17 per cent rock crabs, and 20. I per cent spider crabs. The carapace of these organisms consists of salts and chitin, which is highly resistant to reagents. As the car-apace was found in varying degrees of decomposition, and further since the carapace of crabs and lobsters fed to the fish could not be found in the stomach after four days of digestion, the question arose as to whether the dogfish really did digest chitin. Accordingly, during this summer I began a physiological study of the alimentary canal of Mustelus canis, and extended the work to include the sand shark (Carcharias littoralis) and the spiny dogfish (Squalus acan thias). The experiments of 1904 consisted in the study of the normal contents of the stomach and the spiral valve ; in the determination of the digestive power of the juices contained in the stomach and spiral valve; in the preparation for artificial digestion of extracts of buccal, esophageal, gastric,. and intestinal mucous membranes, and of the extracts of the pancreas; and finally in determining whether or not these fishes digested chitin. During the summer of 195 the work of the previous summer was reviewed, amplified, and extended to include the torpedo (Tetronarce occidentalis), the dusky shark (Carcharhinus obscurusj, the skate (Raja erinacea), and the mackerel shark (Lamna cornubica). More attention was paid to the physiology of the pancreas, middle intestine, and spleen ; and histological preparations were made of the various parts of the alimentary canal from the esophagus to the anus. The r&urn6 of the work is as follows:
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