“…Pettengill & Copeland (1948) found phosphatase in the gill cells of Fundulus, but in his very careful histochemical study of the cells in the guppy, Vickers (1961) could not demonstrate this enzyme. Sexton & Russell (1955) found succinic dehydrogenase in the gill cells of the goldfish, and Maetz (1953) found carbonic anhydrase in acidophils of the gills, pseudobranch and gas gland. Vickers found esterase in guppy gills but his technique was not sufficiently precise for intracellular localization.…”