272 THE VOYAGE OF H.M.S. CHALLENGER. 



is full of fine brown pigment granules (fig. 6, d). They form an apparently continuous 

 pigmented layer at the base of the phosphorescent organ, but the lines of separation of 

 the margins of the cells can be clearly detected with a high power of the microscope 

 (fig. 6). 



The phosphorescent organs are traversed by small blood-vessels (figs. 4, 6), in abund- 

 ance. These vessels may be seen ramifying in the organs when viewed by a strong light 

 in the uninjured fish. They appear to be more or less correspondingly arranged on the 

 organs of opposite sides. The capillary vessels appear to traverse the organs superficially 

 to the pigment-cells and amongst the bases of the rods, since the tips of the rods may be 

 detected as present above them by careful focussing when an organ is viewed from the 

 surface. 



When a portion of a phosphorescent organ is examined with a deep focus from the 

 surface, a network of ramifying pigmented strings and fibres is observed, which lies just 

 above the hexagonal pigment-cells and includes the hexagonal columns in its meshes 

 (figs. 6, 12, 13, 14). The pigmented strings follow mostly the lines of junction of the 

 margins of the hexagonal pigment-cells and thus surround the bases of the hexagonal 

 columns, but they also form long main stems extending for considerable distances in a 

 definite direction, and give ofi" numerous confiecting offsets which may directly cross the 

 hexagonal areas. They also send vertical ofi"sets up between the columns which give off 

 fine ramifications and form partial networks at the surface of the phosphorescent organs, 

 amongst or just below the superficial cells. The strings are very deeply coloured by the 

 presence of dark brown pigment-granules. They show enlargements at their points of 

 junction, and these enlargements contain in their interior small masses of pigment 

 darker than the general pigment. 



Beneath the components of the phosphorescent organs already described is a layer of 

 connective tissue, which contains numerous large ramified pigment-cells such as occur com- 

 monly in the pigmented tissues of other fishes, and which is also traversed by nerves and 

 blood-vessels (figs. 15, 16). I am uncertain whether in the recent condition this connective 

 tissue layer is always in close relation with the under surface of the phosphorescent 

 organ. It is frequently found widely separated from it in my sections, but I think it 

 most probable that, in the recent condition of the animal, it lies closely applied to 

 the floor and against the walls of the phosphorescent organ cavity, with the imder 

 surface of the phosphorescent organ closely applied to and in contact with it. It 

 is shown in fig. 2 as seen in an actual section, where it is detached both from the 

 phosphorescent organ and the floor of its cavity, excepting towards the outer margin of the 

 latter. It is attached towards the middle line to the sides of the ethmoid septum where 

 the latter unites with the ridge of the roof of the skull. No doubt it supplies nerves and 

 blood-vessels to the phosphorescent organs. Blood-vessels are frequently seen in sections 

 attached to the under surface of the phosphorescent organ by parts of the connective- 



