REPOET ON THE DEEP-SEA FISHES. 293 



b. Structure. 



The structure of these organs has been carefully studied by Ussow,' but I cannot here 

 give a review of all his statements. The main results, however, of his examination of 

 CJiauliodus, Astronesthes and Stomias, are the following :— 



The organ consists of two parts, divided from each other by a constriction of the wall. 

 The outer portion is filled by a structureless liquid, the function of which is to protect 

 the tender structures below from the pressure of water. A complicated lens which is 

 composed of cells is situated in the constriction. It is convex in front and drawn out 

 into a cylindrical process behind. 



The lower or internal chamber, which is designated as an eye, is occupied by radial 

 " Krystall Kegel." The spherical base is occupied by ganglion cells and the whole is 

 enclosed by a pigment coat. 



Leydig ^ describes these organs in Ichthyococcus very differently indeed. According 

 to this author both the chambers of the composite organ are occupied by radial gland- 

 tubes filled with the well-known spherical granular cells. In the centre, near the 

 constriction, there is a space filled with a granular mass which is in connection with a 

 stout nerve entering the organ from wathout. 



My own observations made on those of the four species mentioned above, are 

 in accordance with Leydig's (loc. cit.) results. I have not seen anything like the 

 structures described by Ussow in any of the species examined by me. 



Seen from the surface with the naked eye, the organs appear as dark spots with 

 whitish centres. With a magnifying glass circular and oval patches of this kind can be 

 distinguished. In section series we observe the foUo'udng structure. 



The whole organ evidently consists of two parts (PI. LXIX. figs. 2, a, 3, 4 ; PI. LXXI. 

 fig. 32), an interior regularly spherical and an exterior cup-shaped part. The whole is 

 exceedingly regular and appears as a rotation body round an axis, the leading lines of 

 which form three-quarters of a circle for the interior part and a parabola for the external 

 cup-shaped part. 



The axis of this organ is mostly vertical to the surface as in Astronesthes (PI. LXIX. 

 fig. 3), or oblique and inclined to the surface at an angle of 30° as in Opostomias 

 ■micripnus. 



In the latter case the cup-shaped part, which is a rotation-paraboloid, appears cut off 

 obliquely. 



In the first case the organ appears, when seen from the surface, circular, in the second 

 elliptical, otherwise there is no dift'erence between the vertical and oblique composite 

 phosphorescent organs. 



These organs are of pretty uniform size. Usually those at the anterior ends of the 



1 M. Ussow, loc. cit. 2 p, Leydig, Die augenalmlichen Orgaue der Fische, pp. 22-24. 



