Abstract
According to data recorded elsewhere 1 , the following changes in the digestive tube occur in Rana pipiens and Ambystoma tigrinum during metamorphosis.
The rôle of autolysis and phagocytosis in the quantitative reduction of the tissues in the gills, fins, and tail of amphibian larvæ during metamorphosis has been studied repeatedly. Autolysis and phagocytosis also account for a large part of the quantitative reduction in the tissues in the stomach and intestine. The extrusion of tissue elements, especially from the mucosa and submucosa, into the lumen of the stomach and intestine is an additional factor which the writer has not found recorded hitherto.
As the stomach and intestine undergo reduction in length, their walls become thicker. As pointed out by Ratner 2 , the increase in the thickness of the several layers in the walls of these organs is brought about not by active cell proliferation but by rearrangement and aggregation of the elements already present. During the early phases of this process many of the smaller blood vessels become obliterated or constricted; consequently autolysis of many of the tissue elements is initiated. The tissues become infiltrated with leucocytes and phagocytosis, doubtless, plays a part in the removal of tissue fragments.
During the progress of metamorphosis, the stomach and intestine become free from ingested material and masses of cellular debris, including nuclei in which a portion of the chromatin still reacts to the basic stain, olccur in the lumen throughout the stomach and small intestine. The gastric and intestinal epithelium becomes itncreasingly irregtdar as metamorphic changes advacce. The nulclei of all the epithetlid cells no longer remain at alpproximately the same leved, but many of them approach the free surface of the epithelium. Not infrequently the nuclei of epithenal cells protrude and the cells slough into the lumen.
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