Nodules of tissue indistinguishable microscopically from pancreas have been observed by many investigators and have been discussed at length, deservedly, in numerous papers. Not only is such a phenomenon of considerable interest, but it presents a fundamental pathologic problem. In many of the papers that have appeared, not only have hypotheses which are untenable in the present state of knowledge been proposed, but even patently inaccurate observations have been made. In addition, certain relevant features of considerable import in the determination of the nature of these masses have been overlooked. HISTORICAL DATA The earliest record of the occurrence of pancreatic tissue in the stomach which is available to us is that of Zenker, published in 1861. He referred to a previous note by Klob in 1859, and to some observations in lower animals by Leydig (1857). Wagner (1862) and Gegenbauer (1863) reported other cases, and a few further reports appeared,