166 THE POPULAR SCIENCE MONTHLY. 



chidce and Scopelidce (from specimens preserved in spirit), and has con- 

 siderably advanced the solution of the question of the office of these 

 organs. 



The organs in the /Sternojrtychids 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, con- 

 sisting 1. Of eye-like organs ; 2. Of organs of a glass-pearly appear- 

 ance ; 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 Sco2ielus, 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 



Fig. %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 pro- 

 ceeding 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 



