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



The composite ocellar organ with reflector consists of three distinct layers ; an outer 

 layer of pigment, an inner coating of light-reflecting threads or spicules, and a transparent 

 soft mass in the interior. 



The pigment layer encloses the proximal portion and also extends distally with 

 undiminished thickness to the margin of the cup (compare PL LXX. figs. 17-24 ; and 

 PI. LXXII. fig. 44). It consists of dark brown or black pigment-granules closely packed 

 in the connective tissue. 



The reflecting layer, which is perforated and traversed by bloodvessels and nerves 

 leading into the interior of the organ, is very thick and hard. In some cases pigment- 

 granules are found in the course of the bloodvessels and nerves in the perforations 

 through this layer. Such are figured by Emery,^ and have also been found by me iu 

 some cases, and Leydig " records them in the case of Scopelus. 



The light-reflecting layer is composed of calcareous spicules which vary exceedingly 

 in size. They are generally very thin, and may be very long and filiform, or shorter, 

 only about fifteen times as long as thick and abruptly pointed at each end, as in 

 'Argyropelecus. They are closely packed, generally parallel, and are disposed longi- 

 tudinally, extending from the base of the cup to the margin in meridional lines. 

 The spicules are not round, cylindrical, but prismatic, with plane surfaces and accurately 

 apposed to one another, there being hardly room for any substance between them. This 

 intervening substance forming the thin sheaths of the spicules appears as connective 

 tissue. The optical efi"ect of this structure is very remarkable, its lustre being very 

 brilliant in consequence of the flatness of the surfaces of the spicules. 



The structure which occupies the interior of these organs, however, demands our 

 special attention. In the proximal sacs of the complex and the solitary organs, and also 

 in the large ventral canal of Sternoptyx, a glandular structure is met with. This consists 

 of tubes which extend more or less longitudinally throughout the ventral canal of 

 Sternoptyx (PI. LXX. fig. 20), and which appear radially situated in the other cases 

 mentioned above. In these (PL LXX. fig. 23) the gland-tubes are conical, attached to 

 the wall of the sac by their broad base, and opening at the narrow end which lies just 

 below the mouth of the sac. 



These tubes are formed of a fine membrane into which bloodvessels and nerves 

 extend, and are lined by a single layer of highly granular gland-cells, which appear about 

 as broad as high. The lumen is generally occuj)ied liy a granular substance which 

 may be stained very readily, and which appears to be mucus, jirecipitated by the action of 

 spirit. The gland-tubes in the ventral canal of Sternoptyx seem' to open below the 

 bases of the cups in the corresponding position. These gland- tubes do not occupy the 

 whole of the sac, there being an empty space just below the mouth of the sac into which 



' E. Emery, Mittheil. aus d. zool. Station zii Neapel, Bd. v. 



- F. Leyuig, Die augenalnilichen Organe dur Fische, pi. x. fig. 60 



