This paper deals with a neoplastic disease of the common leopard frog. The disease is characterized by the occurrence of more or less circumscribed tumors composed of glandular epithelium in atypical arrangement, and by the frequent presence within the nuclei of the tumor cells of prominent inclusions. One hundred and fifty-eight examples have been studied;2 87 of these were in males, 71 in females. The tumors have been confined to the kidneys except in two frogs in which retroperitoneal tumors were present. The frogs in which tumors were observed were of medium or large size, weighing from 30 to 100 gm.

General Character of the Renal Tumors: All of the tumors are of ivory-white color and slightly firmer in consistency than the renal tissue. They are fairly well circumscribed but never encapsulated. Their shape varies; the smaller growths are usually oval or roughly spherical, the larger ones have no particular shape. Their surface is either smooth or coarsely lobated; no ulceration has been observed. The disease may involve one or both kidneys; there may be a single tumor or more than a dozen separate masses may be present. In Figure 1 are shown a number of photographs of kidneys which illustrate the variation in appearance of the tumors.

1 This investigation has been aided by grants from Mr. William Donner and the International Cancer Foundation, and From the Faculty Research Committee of the University of Pennsylvania.

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