Comparative pathology is rapidly adding much valuable material for our understanding of the biology of cancer, and we are in a fair way toward the establishment of a distinct branch of research in this direction. It certainly is of much significance that cancers, or growths which greatly resemble them, occur in all animal forms, at least in all vertebrates, and are not the unhappy heritage of the human race exclusively. We are coming to realize that not only our common domestic animals may succumb to cancer, but even the cold-blooded animals sometimes suffer the same fate. Typical malignant growths have been described in birds, reptiles, frogs, turtles, salamanders, eels, and especially in fish. Schmey,1 who has recently reviewed the literature, has found reports of fifty-nine cases of tumors in fish, not including the large numbers of thyroid tumors described in certain epidemics in fish hatcheries.