178 THE RADIATING ORGANS OF THE DEEP SEA FISHES. 



straight, prismatic facets (Plate 7, Fig. 37 co) which are parallel to the axis 

 of the organ; they are rounded off distally and drawn out proxinially to 

 points converging towards the distal end of the tubular cavity. The distal 

 ends of these facets lie in a surface convex outwardly and in tolo vertical 

 to the axis of the whole organ. Tlie triangular space outside these facets, 

 between them and the surface, is occupied by gelatinous tissue (gl). 



The small curved facets and the proximal portions of the large straight 

 ones which together occupy the inner part of the paraboloid and form the 

 middle region of the organ (Plate 7, Fig. 37) are clothed with a single layer 

 of cylindrical cells which form a kind of simple epithelium (Plate 7, Fig. 36). 

 These cells take up the greater part of the space within the facet and only 

 leave an exceedingly narrow central canal (Plate 7, Fig. 36 en) free. This 

 canal extends longitudinally in the axis of the facet towards the tubular 

 space in the interior of the organ. Probably it opens into it, as I have seen 

 many indications of such a connection, but I am not certain about it. The 

 cylindrical cells forming the epithelial clothing of these facets and surround- 

 ing the central canal are composed of two kinds of protoplasm. The })roxi- 

 mal three quarters of each cell (lying next the canal) (Plate 7, Fig. 36 ph) 

 are transparent and only slightly stainable ; the distal quarter (lying next 

 the facet wall) (Plate 7, Fig. 36 pt) is granular and takes stains very readily, 

 so that it appears dark and not transparent in the stained sections. In this 

 highly stainable, basal portion of the cell the nucleus (nu) is situated. 



It is probable that the facets of the proximal spherical part of the organ 

 described above contain the same kuid of tissue, but the condition of the 

 material does not allow of this being definitely determined. 



The tissue occupying the distal parts of the large straight cylindrical 

 facets and forming the outer region of the organ (Plate 7, Fig. 37 s) is of 

 an entirely different character. Here we find elongated, slender cells, 

 which are rather indifferent to most stains, but become intensely yellow 

 after treatment with picric acid. In the distal basal part of each of these 

 facets these cells are very slender, spindle-shaped, and arranged longitudi- 

 nally, parallel to the axis of the facet (Plate 7, Fig. 3-t sp). Towards the 

 proximal part they become stouter and shorter and here they often appear 

 club-shaped. The cells appear to rise from the walls of the facet. Those 

 joined to the terminal face of the facet arise more or less vertically ; those 

 joined to the sides arise very obliquely and extend nearly parallel to the 

 facet wall to which they are attached. The cells in the distal part of the 



