Page:Popular Science Monthly Volume 21.djvu/177

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167
THE EYE-LIKE ORGANS OF FISHES.

number of which stream out over the spherical circumference of the sack, and fill the neck-part debouching without, so as to give the figure of a cone of rays sunk into the sphere. The network is, like that of the orange, filled with small cells, a part of them strongly refracting the light, which pass toward the common point of radiation of both divisions into an opaque granular substance. A nerve is always present in the neck-region of this organ, the fibers of which appear to be lost in the granular midst of the spherical section whose exact histological relations have not been ascertained. Externally, the whole organ is inclosed in a lymph-chamber.

The glass-pearly organs are also distributed over the sides of the belly, the head, the gill-flaps, and the skin of the gills, and the three on the skin of the gills are always longer than the others. They are of the shape of a round disk a little sunken, with a body having a metallic

PSM V21 D177 Eyelike organs of the argyropelecus hemigymnus and stomias anguilliformis.jpg
Fig. 3.—Eye-like Organs from the Border of the Belly of Argyropelscus hemigymnus; longitudonal section, greatly magnified. Fig. 4.—Longitudinal Section of the Eye of Stomias anguilliformis (after Dessow), with the parts designated thus; interior vitreous substance (x); lens:(l); retine (r); pigment layer (p); iris-like fold (ir), and optic nerve (n), greatly magnified.

luster and overlaid with a curved transparent integument. An outer brown film of pigment is always present, with a layer of closely joined, regular, hexagonal plates, and a latticed jelly-tissue of delicate, radiated cells that form a network, and are lifted up under a roof-like, spiral-shaped concretion (Fig. 5). The nerve-bundles are also present. Quite similar, but distinguished chiefly by their larger size, is the structure of the so-called luminous organs which are present in the Scopelus Rafinesquii and Scopelus metopoclampus as brightly glittering, well-detined spots above the nasal openings and under the eyes, and which in Scopelus Humooldtii and Scopelus Benoitii exhibit the form and appearance of depressed pearl-spots.