922 



SCANDINAVIAN FISHES. 



that innervates the organ; and the rays of light emitted 

 from the shining mass are reflected, as shown in fig. 

 2.")1, />', ciillec'ted in n cone and concentrated at their 

 exit tlirough the dermal lens. 



These luminons spots" regularly appear, among 

 the fishes now under consideration (see for example 

 our figure of MaiirolicKs MiiUeri), in two rows, an 

 upper anil a lower, along each side of the bodv. In 

 tiieir more liighh- developed form, which consists mainly 

 in the addition of a more powerful reflecting appara- 

 tus'', it is the rule, iiowever, that the upper row breaks 

 u|) lull) two or more groups of 3 — 6 spots gathered 

 in a row, and more or less entirely coalescent inter- 

 nally (\vith the elsewhere sjjherical parts). Similarly 



A B 



Fig. 232. .4: The conHuent lower abdominal spots of Sternoptyx 



(liiijilmiia, twice the natural size, and seen from below. 



fi, ventral fins. After LENDUNFELn. 



Fig. 232. />: Section uf the hiiniiKuis spots shown in fig. A. 

 a, basal canal: b, outer parabolic cups. After Lendenfeld. 



the inner parts of the lumiudus spots in the lo^\•er 

 (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 Arr/i/roj)eh'iiis Olfcrmi. Here the inner 

 ])arts of 12 pairs of luminous sjiots coalesce, forming 

 a common, longitudinal, basal canal (cf. fig. 2.')2, 7?, 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 (ct'. tig. 232, A). 

 i'x'sides the above-mentioned reflecting apparatus, -which 

 lies witiiin the pigment layer, and which here consists 

 of a comparatively thick layer of closely packed and 

 prismatic, calcai'eous spicules, Lendenfeld has described, 

 from the outer (cup-shaped) portions of these organs, 

 cylindrical and ])rismatic 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-shajied, with an oval, liighlv re- 

 fracting body (probably a vesicle) in the thicker, distal 

 end; and these cells, the proximal peduncles of which 

 he sup])Oses to be in direct connexion \\\\\\ tJie nervous 

 fibrils, are in his opinion "the special piiosphorescent 

 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 aie 

 isolated shining spots on the sides of the bodv, on the 

 dorsal or the ventral niargin of the tail, or on the 

 head, especially lielow tlie eyes, on the snout, and on 

 the forehead. The large suborbital spots that occur in 

 certain species are innervated by a special branch of W 

 the fifth pair of cranial nerves. That their function 

 is subordinated to the will of the fish, seems therefore 

 indul)itable. Lendenfeld explains tlicir purpose as 

 twofold: 1) the illumination of tiic w;iter 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 se.xes 

 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 ]);irietal 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 tlie Scopeloid family, Ipnops Murrayi',, whose 



I 



" Composite, ocellar, pliosplioreecent organs, without reflector, Lendknfelo. 



* Composite, ocellar organs, with special reflector, Lendenfeld. 



' fh-iiR, Deep Sea Fish., 1. c, p. l!in, pi. XLIX, fig. B, and MosEi.EY, ibid., App. A, pi. LXVII and LXVIIL 



