922 
SCANDINAVIAN FISHES. 
that innervates the organ; and the rays of light emitted 
from the shining mass are reflected, as shown in fig. 
231, B , collected in a cone and concentrated at their 
exit through the dermal lens. 
These luminous spots" regularly appear, among 
the fishes now under consideration (see for example 
our figure of Maurolicus Mulleri), in two rows, an 
upper and a lower, along each side of the body. In 
their more highly developed form, which consists mainly 
in the addition of a more powerful reflecting appara- 
tus * 6 , it is the rule, however, that the upper row breaks 
up into two or more groups of 3 — 6 spots gathered 
in a row, arid more or less entirely coalescent inter- 
nally (with the elsewhere spherical parts). Similarly 
A b 
Fig. 232. A: The confluent lower abdominal spots of Sternoptyx 
diaphana, twice the natural size, and seen from below. 
a, ventral fins. After Lendenfeld. 
Fig. 232. B: Section of the luminous spots shown in fig. A. 
a, basal canal; b, outer parabolic cups. After Lendenfeld. 
the inner parts of the luminous spots in the lower 
(ventral) row frequently coalesce; and this confluence 
may extend to still more spots, even till the spots on 
one side of the body coalesce with those on the other. 
This is the case, for example, with the luminous spots 
set at the very edge of the belly, in front of the vent- 
ral fins, in Argyropelecus Olfersii. Here the inner 
parts of 12 pairs of luminous spots coalesce, forming 
a common, longitudinal, basal canal (cf. fig. 232, B, a), 
while the outer (distal) parts of each spot (cf. fig. 232, 
B , h) remain independent on each side of the sharp 
median carina of the ventral margin (cf. fig. 232, A). 
Besides the above-mentioned reflecting apparatus, which 
lies within the pigment layer, and which here consists 
of a comparatively thick layer of closely packed and 
prismatic, calcareous spicules, Lendenfeld has described, 
from the outer (cup-shaped) portions of these organs, 
cylindrical and prismatic structures within the refract- 
ing mass (analogous in situation to the above-men- 
tioned gland-tubes). In these structures he distin- 
guished two kinds of radiating cells, one of them 
elongated and club-shaped, with an oval, highly re- 
fracting body (probably a vesicle) in the thicker, distal 
end; and these cells, the proximal peduncles of which 
he supposes to be in direct connexion with the nervous 
fibrils, are in his opinion “the special phosphorescent 
elements”. 
These more highly developed luminous spots appear 
not only on the sides of the body in longitudinal rows, 
but also on the halves of the lower jaw and on the 
branchiostegal membrane. The largest of them are 
isolated shining spots on the sides of the body, on the 
dorsal or the ventral margin of the tail, or on the 
head, especially below the eyes, on the snout, and on 
the forehead. The large suborbital spots that occur in 
certain species are innervated by a special branch of 
the fifth pair of cranial nerves. That their function 
is subordinated to the will of the fish, seems therefore 
indubitable. Lendenfeld explains their purpose as 
twofold: 1) the illumination of the water round the 
fish, whether their possessor be seeking food in the 
dark abysses of the ocean or at the surface in the 
night-time — possibly too as a signal between the sexes 
during the spawning-season — 2) the intimidation of 
a pursuing enemy, when a sudden flash of light may 
save the fugitive. The latter interpretation applies in 
particular to the luminous spots situated on the hind 
part of the body. 
The parietal organ of Amphibians and reptiles, 
according to our present knowledge of its structure, 
seems also capable of explanation as a luminous spot. 
The largest luminous spots known are found in a deep- 
sea fish of the Scopeloid family, Ipnops Murrayi c , whose 
° Composite, ocellar, phosphorescent organs, without reflector, Lendenfeld. 
6 Composite, ocellar organs, with special reflector, Lendenfeld. 
c Gthr, Deep Sea Fish., 1. c., p. 190, pi. XLIX, fig. B, and Moseley, ibid., App. A, pi. LXVII and LXVIII. 
