LAMPROGRAMMUS ILLUSTRIS. 175 
Lateral line as wide as the orbit, extending back on about eighty scales 
to a point below the seventy-fifth dorsal ray. It might be described as 
apparently composed of two systems; the ordinary one below and through 
the scales, and a luminous system outwardly resembling a dermal tube cov- 
ered by about eight series of smaller very thin scales and applied to the out- 
side of a couple of series of the larger scales of the flank two or two and one 
half scales from the base of the dorsal fin. This tube, Plate XXXIV. fig. 
4, contains mucus and against its inner wall a series of narrow, spindle 
shaped, vertically placed, glandular light or flash organs, Plate XXXIV, 
fies. 1, 3, 4, 5, connected with one another by a fine nerve-like strand of 
tissue. Each of the luminous organs is fusiform, somewhat flattened, taper- 
ing at each end and enlarged in the middle, where it contains an elliptical or 
rounded body, disk or facet, of different structure, Plate XXXIV. fig. 5. 
From each end of the spindle the tissue appears to be reflected around the 
wall of the tube over the gland so as to form a complete ring. While the 
skin and scales covering the structures present a black appearance in the col- 
lapsed condition both are so thin as to offer little obstruction to the passage of 
light when the tube is distended by mucus. On Lamprogrammus mger, Alcock, 
1891, Ann. Mag. N. H., VIII, 34, describes loopholes over the glands; no 
such openings are to be seen on the present species. The pores in places 
appear to open along the lower edge of the tube away from the organs. 
Each organ of the series rests on a large scale twice as wide as those at each 
side of it and separated from similar organ-bearing scales by a pair of the 
ordinary scales of the flank, half as large, Plate XXXIV. fig. 4. Thus the 
light organs on this species are not on contiguous scales, as figured on L, mger, 
in the Annals and Magazine, 1891, VII., p. 33, or in the Illustrations of 
the Zoology of the “ Investigator,” 1892, Plate I. fig. 2; the differences will 
be prominently shown by comparison of the mentioned illustrations with 
Plate XXXIV. of the present work. It is most likely that the large scale 
bearing the spindle was originally an ordinary small scale which has so 
enlarged as to cover its neighbors in the next series. The body between the 
lateral systems of the two sides is thinner than either above or below them ; 
this gives rise to the groove-like depressions occupied by the lines. Behind 
the line on the tail the groove disappears and the squamation is irregular. 
The luminous system originated on the head and gradually extended back- 
ward over the body; the arrangements of the scales are sufficient evidence 
that it is a later development. 
