S06 THE VOYAGE OF H.M.S. CHALLENGER. 



I think that these cells are the special phosphorescent elements. I have found the 

 same cells in a good many other kinds of phosphorescent organs of fishes, but not in 

 all of them. 



c. Innervation. 



According to Leydig ^ thick nerves extend through the superficial tissue of the fish 

 below these organs, and give ofi" stout branches, which enter the proximal, sac-shaped, 

 glandular portion from the side. 



According to my own observations the nerve enters at the incision between the sac- 

 shaped and distal cu^D-shaped parts and extends principally below the S2)icule-layer under- 

 lying the latter; there the nerve fibres form a very conspicuous plexus (PI. LXXII. 

 fig. 44, g) which occupies the space between the continuous pigment-layer and the light- 

 reflecting spicule-layer. 



From this plexus nerves are given off" which, together with bloodvessels, traverse 

 the organ perpendicularly from the bottom to the roof, extending upwards in the 

 central pillars of the cylinders of radiating cells described above. They are, as stated, 

 probably in direct communication with the typical phosphorescent clavate cells. 



According to Leydig^ the nerves form a plexus loithin the phosphorescent tissue in 

 the organs of Scopelus humholdtii. 



d. Function. 



Regarding the function of these organs, we are in a more fortunate position than in 

 regard to most of the other structures described in this Appendix, inasmuch as direct 

 observation has shown that these organs actually emit light, so that there can be no 

 doubt about their phosphorescent nature. 



Willemoes Suhm^ says that a Sco2)elus bi'ought up by the trawl at night " shone like 

 a star in the net." Guppy* and Giinther have made similar observations. Gupp)'^ 

 particularly was able to observe that the light is emitted y^-om these organs. 



It seems not improbable that the glands in the sac-shaped proximal portion of these 

 organs produce a secretion which is poured out into the cup-shaped distal part, and there 

 a mutual chemical action between this slime, in which also cells and nuclei are found, 

 and the tjrpical phosphorescent clavate cells may take place at the will of the fish, and a 

 certain amount of light may be produced, which is reflected by the parabolic spicule-layer, 

 and thrown out as a strong flash. 



The ventral organs can illuminate the dark water below the fish for any purpose, 



' F. Leydig, Die augenahiilichen Organe der Fische. 



- F. Leydig, loc. cit., pi. x. fig. 60. 



3 Willemoes Suhm, Clialleiiger-Briefe, Zeitschr.f. wiss. Znol., Bd. .\xiv. 



•• Guppy, Ann. and Mag. Nat. Hist., ser. 5, vol. ix. ' 



