REPORT ON THE DEEP-SEA FISHES. 317 



appear as two pairs of suljorbital organs, an anterior and a posterior. The anterior 

 patches are about twice as large as the posterior, and their outline is ii-regularly lobate. 

 With a magnifying-glass a radial structui'e can be detected in the patches {PI. LXIX. 

 fig. 11). In sections we see that the whole organ is composed of cylindrical gland - 

 tubes of uniform width, which commence at the anterior margin and extend to the 

 posterior end, which is slightly drawn out. The organ is sunk in the surface, so that 

 its upper side lies at the same level as the surrounding surface (PI. LXIX. figs. 12, 13). 

 Near the anterior margin it has the greatest depth, and from this region the floor rises 

 gradually towards the posterior margin (PI. LXIX. fig. 13). It is covered on the outer 

 side by a thin, transparent epithelium, whilst the gland -tubes, which extend from 

 the bi'oad to the narrow end of the wedge-shaped organ, have an inner coating of cells 

 which are about as high as broad (PI. LXIX. fig. 14, h). A narrow lumen is left in the 

 centre of the gland-tube, and this is filled by the slimy secretion, precipitated in granular 

 form by the action of the spii-it (PI. LXIX. fig. 14, c). A special membrane can be 

 observed enclosing each gland-tube (PI. LXIX. fig. 14, a). Between the gland -tubes 

 bloodvessels and nerves, extending mainly in a longitudinal direction, parallel to the 

 tubes, are found. 



The number of gland-tubes in the thick anterior portion is much greater than in 

 the narrow posterior part, where they lie side l)y side, forming a single layer (PI. 

 LXIX. fig. 12). The floor of the organ is formed by a thin, light-reflecting membrane 

 backed by the usual pigment layer, but as in the organs described above from the sides of 

 the body of Astroncsthes, the lower jaw of Stenwpii/x, the gills of Ilalosavms, and the 

 barbels of Opostomias and other fishes, no typical phosphorescent gland-ceUs have been 

 observed. 



(2) Opostomias micripnus. — In this species a single phosphorescent organ is found 

 on each side of the head just below and a little behind the eye. It aj^pcars, when seen 

 from the surface, as a slit (PI. LXXII. fig. 39, d) commencing below the eye and extending 

 backwards and slightly downwards. This slit is 12 mm. long and in the centre 2 mm. 

 wide. In the anterior quarter of it a small white patch — an aperture — is seen in the 

 gray, pigmented, soft membrane which covers the slit. It appears that this membrane 

 is movable, the underlying phosphorescent organ emitting its light through the aper- 

 ture. The margin of the gray membrane adjoining the pore is soft and movable, 

 covering the underlying organ more or less like a lid. The aperture may be con- 

 tracted, so as to screen that organ partially or entirely, or on the other hand 

 dilated and opened wide, leaving a large aperture through which it becomes visible. In 

 PI. LXXII. fig. 39 this aperture is drawn, as it appears in the spirit specimen, in 

 a very much contracted condition. 



The phosphorescent organ which lies below this membrane is a very remarkal)le 

 structure (PI. LXXII. fig. 40). It consists of a lamella abruptly folded in the middle so 



