The finding of tissue cells of another type than those normally found in an organ of the body is always intriguing, and the explanation of such an occurrence presents many difficulties. It is not strange that differences of opinion have arisen as to the exact mechanism by which such a metamorphosis of tissue cells has been produced.
Such changes are found not infrequently in the epithelium of the urinary tract, where they present an interesting urologic study. In this discussion I am confining my attention to the changes occurring in the renal pelvis, the ureters and the bladder. Although the epithelium of these organs possesses a different derivation embryologically, that of the ureter and pelvis being mesodermal and that of the bladder partly entodermal and partly mesodermal, they are all lined with transitional cell epithelium, and, except perhaps in the immediate neighborhood of the bladder outlet, true glands are not