920 



SCANDINAVIAN FISHp;S. 



I AM. S C P E ]. I D JE. 



Form of the hodi/ ruriahle, f/fiieiydli/ HeniH(/-l/ke Iml aho Irref/iihir {sfrom/I// compressed and deep). Scales, irhere 

 l^resent, ih'm, middle-sued or larf/c. Sides of the body {it) all the Scandinavian forms bat one") famished uith 

 luminous spots. Dorsal margin of the tail furnished irith an adipose fin. Margin of the upper jaw formed 

 either hji the inteniiarillaries alone or partlg {behind) bi/ the ma.rillaries as u-ell. Xo barbels. Air-bladder, nhere 

 present, simple and irilJioaf connexion with the cranial laritg. Branchial ciiritg (in all the Scandinarian forms) 

 furnished with jyseudobraiichiic. Ovaries iritli oviduct. 



Most of tlie fislu's Ix'lDiiiiing to this family hfiAe 

 a coiunion characteristic wiiich is connected with their 

 raannei' of life, and of which we have seen no instance 

 ainon^ the preceding' tishes. Nearly all the Scandi- 

 navian Scopeloids and most of the others possess or- 

 gans by means of ^vhich they more or less voluntarily 

 emit a phosphorescent light, and wliich 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 {Lamptiris) 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', though the more 

 copious secretion thereof produced by irritation is sub- 

 ject to the control of tiie nerves. Among tishes 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 tishes special ner\e.s have been found 

 whose extension in these organs suggests that the light 

 radiates in the direction chosen by tiie 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 

 tishes, Batrachians, and reptiles. Together with tlie 



said organ they have been included among so-called 

 ocellate organs; and where it has been declared ^^■ith 

 certainty' that a, special nerve for such an organ nught 

 be traced, their function may best be compared \o that 

 of electric or pseudoelectric organs, i. e. that, as ner- 

 \ous force by means of tine nerve ramifications upon 

 a so-called electric plate excites electricity in a tinelv 

 granular mass (a transformation of the sarcoplasma of 

 a muscular cell) on each side of an elastic plate (a 

 transformation of the rhabdia — rod-sul)stance — of a 

 muscular cell), so the nervous force of the luminous 

 spots, by its action upon a strongly refractive and co- 

 agulant mucus (a ti'ansforraation of cells in a slime- 

 gland of the skin), causes this mucus to burn and shine. 

 In their simpk'st furm the luminous spots are de- 

 scribed by Lendenfei,!)'' 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 — O'-^ mm. in 

 diameter) witli a laver of pigment within their ba.se. 

 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 iinier surface is lined on the outer part (distally) 

 with a \[\\f>v of closely packed fusiform cells, at right 

 angles to the skin, and on the inner part (proxinially) 

 with a layer of gland-tulics, arranged in a similar 

 concentric manner and closelv ])ackcd. These tul>es 

 ai'e closed and rounded at the basal (|)roximal) 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 



" The obscure and extremely rare ^tidis atlanticus. 



'' BoiE, Isis 1827, p. 72G. 



' GUNTHER Drep Sea F/.s7j., Hup. Voy. Challeng., Zool., vol. XXII, App. B. 



