920 
SCANDINAVIAN FISHES. 
Fam. SCO PE LID M. 
Form of the body variable, generally Herring-like but also irregular (. strongly compressed and deep). Scales, where 
present, thin , middle-sized or large. Sides of the body (in all the Scandinavian forms but one a ) furnished with 
luminous spots. Dorsal margin of the tail furnished with an adipose fin. Margin of the upper jaw formed 
either by the intermaxillaries alone or partly (behind) by the maxillaries as well. No barbels. Air-bladder, where 
present, simple and without connexion with the cranial cavity. Branchial cavity (in all the Scandinavian forms ) 
furnished with pseud obranchiw. Ovaries with oviduct. 
Most of the fishes belonging to this family have 
a common characteristic which is connected with their 
manner of life, and of which we have seen no instance 
among the preceding fishes. Nearly all the Scandi- 
navian Scopeloids and most of the others possess or- 
gans by means of which they more or less voluntarily 
emit a phosphorescent light, and which are therefore 
known as luminous spots. As a physical reflex or a 
chemical phenomenon such phosphorescence is found 
in certain plants; as a real manifestation of a vital 
function it is not uncommon in the animal kingdom. 
Many — if not most — of the lower and the lowest 
marine animals are phosphorescent; and among the 
higher evertebrata the glow-worm ( Lampyris ) is familiar 
to us all. In the glow-worm the light extends not 
only to the fatty bodies in the abdomen, but also to 
the eggs, i. e. the fat of the yolk, and consequently 
this phenomenon — in the last case at least — is not 
unconditionally an attendant of nervous activity. Nor 
is this the case with the light that radiates from the 
dermal mucus of certain Batrachians 6 , though the more 
copious secretion thereof produced by irritation is sub- 
ject to the control of the nerves. Among fishes too, 
in some of the organs more highly developed for phos- 
phorescent purposes, the light seems to be at least par- 
tially independent of the immediate action of the will. 
But in some fishes special nerves have been found 
whose extension in these organs suggests that the light 
radiates in the direction chosen by the fish and at the 
moment when the fish desires its aid. 
In their more developed forms the luminous spots 
closely resemble the so-called parietal organ of lower 
fishes, Batrachians, and reptiles. Together with the 
said organ they have been included among so-called 
ocellate organs; and where it has been declared with 
certainty that a special nerve for such an organ might 
be traced, their function may best be compared to that 
of electric or pseudoelectric organs, i. e. that, as ner- 
vous force by means of fine nerve ramifications upon 
a so-called electric plate excites electricity in a finely 
granular mass (a transformation of the sarcoplasma of 
a muscular cell) on each side of an elastic plate (a 
transformation of the rhabdia — rod -substance — of a 
muscular cell), so the nervous force of the luminous 
spots, by its action upon a strongly refractive and co- 
agulant mucus (a transformation of cells in a slime- 
gland of the skin), causes this mucus to burn and shine. 
In their simplest form the luminous spots are de- 
scribed by Lendenfeld 0 as depressions or elevations of 
the skin, scattered or distributed in rows on the sur- 
face of the body, the smaller (0‘1 — 0'3 mm. in dia- 
meter) without pigment, the larger (0‘3 — 0'5 mm. in 
diameter) with a layer of pigment within their base. 
They are then covered only by the thin epidermis, and 
are furnished with nerves and fine capillary vessels 
from the skin. Internally they are indeed hollow; but 
the inner surface is lined on the outer part (distally) 
with a layer of closely packed fusiform cells, at right 
angles to the skin, and on the inner part (proximally) 
with a layer of gland-tubes, arranged in a similar 
concentric manner and closely packed. These tubes 
are closed and rounded at the basal (proximal) end, 
open towards the centre of the organ, and full of gland- 
cells, which secrete the granular mass that fills the 
hollow in the centre. This mass, a strongly refractive 
and coagulant slime, is produced by an immediate 
a The obscure and extremely rare Sadis atlanticus. 
b Boie, Isis 1827, p. 726. 
c Gunther Deep Sea Fish., Rep. Voy. Challeng., Zool., vol. XXII, App. B. 
