ASPECTS AND ETIOLOGY OF CARCINOMA 59
neighbourhood of the stomach in connection with the yolk-stalk. Undoubtedly, many of these germ-cells degenerate, and few, if any, of the vagrant ones, after a certain early period, ever find their way to the germinal nidus. The embryomata of Wilms are to be regarded as products of such vagrant or of persistent (in ovary or testis) primary germ-cells. But—and this is remarkable
—very many such vagrant germ-cells occur in places where embryomata are not usually encountered thus, in the immediate neighbourhood of the stomach, in the liver, in or under the skin and in the rectum. In nearly every embryo one or more germ-cells may be found in the yolk-stalk, in the immediate neighbourhood of the pylorus, and also in the rectal epithelium.
It may therefore be suspected that if the germ-cells of many of these places—e.g., liver, pylorus, rectum, etc.— ever do develop, they must give rise to some product not of the nature of an embryo, not an “emhryoma.” it is not without interest that the common situations for the origin of cancer are the very ones in which vagrant germ-cells are usually met with thus, in the rectum, near the pylorus (yolk-stalk), other parts of the gut, in the kidneys, in the skin, etc. Apparently, cancer of the tongue, of the esophagus, of the larynx, and of the mammary gland, at first glance form exceptions, but this is not really so. Tongue, esophagus, and larynx are products in the higher forms of a rebuilding of the gill-region esophagus and mammary glands are closely associated with the pericardium, where vagrant germ-cells (and at times embryomata as products of these) are often found. That cancer should arise in what embryologically are holes and corners—places where layers and folds come together, as in tongue and larynx—is readily explicable. Such vagrant germ-cells are intruders in the situations