NUPTIAL tubercles appear as male adornments in many species of fishes at the mating season. Hypertrophy of epidermal cells in minute patches gives rise to the tubercles which commonly occur on the fins, head or body (e.g. Barbatulus, Catostomus, Moxostoma, Carassius, etc.), or a similar but more extensive hypertrophy leads to the formation of thickened pad-like areas (e.g. Pimephales). Such structures are generally considered as purely male developments. It is therefore of value to record that while examining sections of the skin of gravid male and female smelt, Osmerus mordax (Mitchill), it was found that a similar hypertrophy of epidermal cells in minute patches is present on the females as well as the males of this species. The development of tubercles in the female is barely visible to the naked eye, while the male is obviously and richly adorned. Kendall (U.S. Bur. Fish., No. 633, 1908) has briefly noted the presence of epidermal tubercles distributed generally on the head and body of a single mature male smelt found dead on the shore of Lake Champlain. Specimens of 0. mordax seined at the outlet of Lac Brule, Province of Quebec, late in April, 1933, were preserved by Mr. G. Prevost and later sent to me for identification since the appearance of these specimens was markedly altered from the usual owing to the great development of tubercles. The collection consisted of eleven mature males ranging in length from 11.0 to 12.2 cm., and a single gravid female 11.5 cm. long. The specimens were heavily coated with mucus, and while removing this from the female I noted the presence of minute white patches scattered over the dorsum of the head. The appearance was that of an attack of ichthyopthiriasis, and having an interest in that disease at the time, I sectioned a small portion of the skin. Later, I obtained additional specimens of gravid females from Lake Memphremagog, and in this material as well similar patches were present on the head, and were also detectable in sections of the skin from the back alongside the dorsal fin but not elsewhere on the body. Small portions of the skin from the top and sides of the head and of the body, as well as parts of the pectoral, pelvic and dorsal fins were removed from male and female specimens, sectioned and examined. In the normal condition, the stratum germinativum of the skin rests upon a thick layer of compact connective tissue and consists of the usual columnar cells with ovoidal nuclei (8tu by 3,u) placed with their greatest axis at right angles to the surface of the skin. Peripheral to this there is an intermediate layer of transitional squamous cells with subovoidal (6,u-8ta by 3jt) nuclei, and most superficially two or three layers of squamous cells with compact elongate nuclei (3,A long) lying parallel to the surface of the epidermis. The number of cell layers forming the epidermis differs on the various regions of the body, the epidermis being thickest on the head and back where there are twelve to fifteen layers of cells all together, thinner on the sides of the body, and thinnest on the fins where the total number of cell-layers is only