EEPORT ON THE DEEP-SEA FISHES. XXVU 



to the original one which the muciferous system fulfils in the ordinary type of surface 

 fishes. Considering that the majority of the localised and more highly specialised 

 luminous organs are situated within the area of, and stand in relation to, the muciferous 

 system, we may be justified in assuming that one of those additional functions is to 

 surround the fish with luminosity, the more so as the mucus has been actually observed 

 to have phosphorescent properties in newly caught specimens. 



The so-called phosphorescent organs or luminous bodies have been noticed ever since 

 the first species of Scopelihs and other pelagic genera were described ; ])ut they were 

 regarded as j^eculiar pigment spots or modified portions of the scales. Many species of 

 Scojyelus possess, beside the round mother-of-pearl-coloured spots, a pair of whitish gland- 

 like bodies on the upper side of the snout ; and it seems that Cocco was the first to 

 assert that these bodies have phosphorescent properties. He mentions^ these organs as 

 " apparecchio lucido," and one of the species possessing them he named " Nychtophus 

 metopoclampiis." Bonaparte copied Cocco's accounts, and Valenciennes* adopted his 

 views as to the function of these organs. In 1864, when engaged in the systematic 

 arrangement of the fishes of the families Sternoptychidse, Scopelidas, and Stomiatidaj, I 

 ascribed phosphorescent properties to all these organs, whilst from their histological 

 examinations Leuckart" and Ussow'' declared them, or at least part of them, to be 

 accessory eyes. Leydig^ holds the opinion that they are " pseudo-electric " organs, which 

 sometimes may have the function of emitting light ; Emery" adopts the view of their 

 phosjihorescent nature in Scopelus. As these organs occur, not only in deep-sea fishes, 

 but also in nocturnal pelagic forms, their function miglit have been expected to be readily 

 ascertained by actual observation ; however, so far as I am aware, this h;xs been done 

 twice only, viz., by myself, when I happened to notice distinct flashes of light to issue 

 from a dying specimen of Scopehis floating on the surface in the British Channel ; and 

 by Dr. Guppy,^ who examined some freshly caught specimens of the same genus. 



During my examination of the Challenger fishes I found the luminous organs widely 

 distributed over the various organs of the body, and discovered esi)ecially their presence, 

 in a unique modification, in a genus of AlciJocephalid fishes [Xenodeniiichthys), as weU 

 as in the Halosauridae, in which their relation to the muciferous system is undeniable. 

 Finally, Liitken* suggested that the white terminations of the dorstil tentacle of Hlmanto- 

 lophus reiiihardti may be phosphorescent during life, which undoubtedly they are. 



Luminous organs are not equally distributed among the various families of deep-sea 



' Nuovi Ami. d. Sci. Xat., 1838, tom. ii. p. 184. 



2 Cuv. Val., vol. xxii. pp. 443, 444, 445. 



3 Ueber muthmassliche Nebenaugen bei einem Fische, Berichl u. d. Versamml. devisdi. Naturf., 18C4. 

 * Bull. Soc.imp. dcs Nat. Moscou, 1879, vol. liv. p. 79. 



5 Die augeneihnlichen Organe der Fische, 1881, 8°, Bonn. 

 » Mittheil. Zool. Slat. Neapel, vol. v., 1884, p. 471. 

 ' Ann. and Mar/. Kat. Hust., vol. ix., 1882, p. 202. 

 ' Vidensk. Selsk. Skriv., vol. xi., 1878, p. 341. 



