our recognized sensorial functions, but rather point to some sixth sense, unknown to us. To this class belong the phenomena presented by a group of bony fishes, living for the most part at extreme sea-depths, classified in the three related families of the Scopelids, Sternoptychids, and Stomiatids, which have lately received attention from naturalists. They are generally small fishes, often only an inch or less in length, and have on either side of their belly a row of bright spots, extending from the snout to the tail, that might be said to look like a double row of pearl-buttons fastened upon their skin-coat. Sometimes a third row is found extending from the head to the anal fin; and frequently single spots, often of considerable size, are scattered over the head and gills and over the sides of the fish. Several ichthyologists—among them B. Rafinesque, of Palermo; Delle Chiaje, of Naples; Risso, of Nizza; and Cocco, of Messina—have had their attention drawn, since the first decade of the century, to specimens of those creatures that have occasionally been washed ashore in storms; and the more recent deep-sea investigations have made several allied forms known. The old ichthyologists apparently never examined the spots very carefully, but simply described them as silvery mottles or light points. Leuckart seems to have given them the first critical examination in 1864, in Chauliodus Sloani, Stomias boa, and Scopelus Humboldtii, and came to the opinion from it that they might possibly be regarded as supplementary eyes. Ussow, of Moscow, published a paper in 1879 on the structure of the so-called eye-like spots in Chauliodus, Stomias, Astronesthes, Gonostoma, and Maurolicus, in which he expressed the conclusion that the spots in the
Fig. 1.—Argyropelecus hemigymnus, twice the natural size.
three first-named genera were real organs of sight, but that the structure of those in the other genera was of a quite different nature, and really glandular. In the same year Leydig published a work on the Chauliodus Sloani, in which he admitted the similarity of the spots of that species to eyes, but was disposed to regard them as transitional organs rather than as real eyes, and referred to one of his observations as indicating that they might have been luminous in life. Leydig has more recently examined ten other species of the families Sternopty-
