THE RADIATING ORGANS OF THE DEEl^ SEA FISHES. 193 



connective-tissue sheath enclosing the whole organ. The upper portion of 

 this pigment sheath forming the roof of the upper part is dome-shaped, the 

 lower portion, forming its floor and separating it from the lower spherical 

 part, is flat or even a little concave. At the circular line where the upper part 

 joins the lower a conspicuous ring-shaped thickening of the pigment layer 

 (pt) is observed. From this a small annular ridge extends outwards and 

 downwards, forming the rudiment of a cup enclosing the basal, upper portion 

 of the lower, spherical part of the organ. 



The interior of the upper part of the organ is traversed by a horizontal, 

 strongly pigmented membrane (pm), which divides it into a larger upper 

 and a smaller lower chamber. In both these chambers large cavities (cv) 

 are seen. In the upper one there seems to be only one such cavity. This 

 is situated ventrally and surrounded by a special endothelial cell layer, 

 separating it from the transparent connective tissue occupying the dorsal 

 and lateral parts of the upper chamber. In the lower chamber more 

 cavities than one are seen. These lie dorsally. Below them in the ventral 

 part of this chatnber large sinuous blood vessels (b) extend. 



The lower part of the organ (B) is covered dorsally by the pigmented 

 floor of the upper part of the organ and the annular rudiment of a pigment 

 cup referred to above. Laterally and ventrally it is surrounded by the 

 transparent connective-tissue sheath only. From the middle of the roof 

 of this lower spherical part of the organ a cylindrical thread composed of 

 connective tissue (z) arises which extends vertically downward to its centre. 

 This thread is composed of longitudinally arranged, spindle-shaped connec- 

 tive-tissue cells with oval nuclei. Along this thread blood vessels (b) and 

 probably also a nerve extend from above down to the centre of the sphere. 

 The lower end of the thread is thickened to form a terminal knob in which 

 a sinuous cavity, filled with blood corpuscles, is observed. Apart from this 

 thread with its terminal knob the whole of the sphere is occupied by large 

 radially arranged conic cells (pc) equal in length to its radius. In arrange- 

 ment and structure these cells are similar to the conic elements in the inner 

 region of the compound organs of Clicmliodus iar^«/i<s. described above. 

 They are, however, more slender. The inner seven eighths are occupied by 

 finely granular, transparent protoplasm not readily stainable ; in the outer 

 eighth of the length coarser grained protoplasm showing great affinity to 

 hoematoxylin and other stains is observed. In the peripheral part of each 

 cell one small, spherical nucleus is situated. 



13 



