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



)8. Histology. 



( 1 ) The scales. 



The scales have been described by Dr. Giinther elsewhere in this Report, they do not 

 show any peculiarity so far as their histological structure is concerned. 



(2) The pigmented metnbranes. 



The pigment does not form a perfectly continuous layer, but appears in patches, which 

 lie pretty close together so that these membranes have a dotted appearance. They 

 surround the scales on all sides (PI. LXXIII. figs. 61, I, m, G2, c,f). 



(3) The light-reflecting membrane. 



The outermost layer of the scales is a veiy thin light-reflectiug membrane, which 

 appears in sections as a narrow dark line only, it is closely attached to the pigment- 

 meml)ranc below it (PI. LXXIII. figs. 61, n, 62, h,f). When seen from the surface 

 (PI. LXXIII. fig. 54) it appears to be composed of two systems of very fine parallel 

 threads crossing each other nearly at right angles. This structure is exceedingly minute 

 and becomes apparent only under a very high power, and it seems probable that the 

 silvery lustre which these membranes exhibit is produced by this structure. 



(4) Tlie phosphorescent organ. 



The elongate spindle-shaped phosphorescent organ above mentioned appears to Ik* 

 connected with the tissue below by a comparatively slender canal, which passes through 

 an oblique perforation in the scale. It is rich in bloodvessels and consists essentially 

 (if two parts. In the lower portion we. find numerous and large bloodvessels, whilst 

 l)etvveen these and outside of them veiy elongate radially extending cells are situated, 

 which reach from the base of the organ to the surface. Here they are curved so that 

 their distal portion extends tangeutially. These cells are mostly spindle-shaped, 

 granular, and contain a nucleus in the centre, and between them comparatively wide 

 transparent spaces are observed. It seems that these spindle-shaped cells are not in 

 contact, but divided from each other by a hyaline substance. The outermost layer of the 

 organs is as usual more granular than the remainder. In the middle of the organ these 

 s])indle-cells are vertical to the surface, but near the margin they curve outwards. At 

 the base of the spindle-cell layer irregidar ganglion cells are found. The whole organ is 

 raised above the surface of the scale, but it is covered and protected from tlie outside 

 by the above mentioned membranes. 



