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Page:Popular Science Monthly Volume 21.djvu/176

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166
THE POPULAR SCIENCE MONTHLY.

chidœ and Scopelidœ (from specimens preserved in spirit), and has considerably advanced the solution of the question of the office of these organs.

The organs in the Sternoprtychids and the Scopelids show essential differences in structure, and a third type has been noticed in some scopelids. Hence, Leydig has described three classes of organs, consisting—1. Of eye-like organs; 2. Of organs of a glass-pearly appearance; and, 3. Of luminous organs. These three forms can be easily distinguished with a glass. The organs of the first class resemble brownish sacks filled with a gray matter; those of the second class brown-bordered, plate-shaped depressions, the ground and edges of which are covered by a film with a metallic luster; and those of the third class, confined to the genus Scopelus, present themselves as larger spots of a silvery luster, or a grayish pearl-color.

The eye-like organs—which we have already spoken of as arranged in rows along both sides of the lower central line of the body—are also found on the head about the nose and eyes, on the lids and skin of the gills, and, in the genus Chauliodus, in groups of much smaller spots within the cavities of the mouth and gills. The number of the spots, which hardly ever exceeds a hundred in the other genera, rises in this genus to a thousand and more. Their outward appearance is not quite the same in the different parts of the body, but passes from the form of a round sack to that of a cylinder; and some spots are of the shape of a bell or an ampulla. In the genus Argyropelecus (Fig. 1) the Organs are grouped. They consist of an integument of brown

PSM V21 D176 Ichthyococcus ornatus.jpg
Fig. 2.Ichthyococcus ornatus, twice the natural size.

pigment, which is coagulated from the thick skin and forms a ring-fold, or gather, dividing the interior into a forward and hinder part. Within this integument is a film of a bright metallic luster, which either underlies the whole of it, or only forms a belt at the mouth, and consists of iridescent threads or spangles lying in the thick skin. The gray inner mass is divided into two sections, a larger hinder part filling the sack, and a smaller forward part. The hinder part is always spherical, the forward part cylindrical, and the two together form a connected whole. To both parts appertains a radial striation proceeding from a frame-work that is continued within from a membrane inclosing the gray mass. The longitudinal section of the hinder part of the organ superficially resembles the cross-section of an orange. We have to deal here, however, not with a few pervading radiations, but with a hollow cone of radiations meeting in the center, a certain