Art. XII.—Note on the Occurrence of Cancer in Fish. By Professor Scott. [Read before the Otago Institute, 9th June, 1891.] Plate XVIII. The fish afflicted with this disease were all specimens of the American brook-trout (Salmo fontinalis) kept in confinement in one of the ponds at Opoho belonging to the Dunedin Acclimatisation Society. Males and females were alike affected, and the diseased fish never recovered. Through the kindness of Mr. Deans, the manager, I was able to examine several specimens showing the disease in various stages of advancement, and the following is a short account of the naked-eye and microscopic appearances of the growth. In the earliest stages the ventral wall of the pharynx in the middle line, a short distance behind the tongue, is seen to be somewhat roughened, and raised in low irregular swellings. At this stage nothing is to be seen unless the mouth is opened widely. As the tumour grows, however, not only does it involve more and more of the pharyngeal floor, spreading also to a slight extent laterally, and involving the ventral ends of the gill-arches, but it ultimately shows itself externally as a rounded pink lump on the isthmus in the angle between the diverging branchiostegal rays. A microscopic section of the tumour shows all the stages in the development of a carcinomatous growth. In parts a purely glandular structure is seen—the glands apparently of the acino-tubular type. Elsewhere, owing to proliferation of the cells, the gland acini have become distended and irregular in form (adenoma stage), while in large areas these over-distended acini have, as it were, burst, and the liberated cells, making their way into the stroma, infiltrate it, and all gland-structure is lost (carcinoma stage). Of the two figures which accompany this note, the first (P1. XVIII., fig. 1) shows the floor of the mouth and pharynx, as seen from above, of a fish suffering from the disease. The nodular character of the tumour is clearly seen. The second shows a small portion of a section as seen under the microscope. A distended acinus is seen liberating a stream of cells into the gland stroma (fig. 2). The occurrence of cancer in the lower animals has been frequently noted of late years, and it is by no means so rare among them as it was at one time thought to be. I have, however, been unable to find any mention of its having been noted in fish.