REPORT ON THE DEEP-SEA FISHES. 287 



orgau itself, and is only lower and flatter in proportion. This space is not altogether 

 "empty" as the expression "empty space" might imply, for it appears filled by a 

 finely granular mass, evidently the secretion of the tubes containing the granular cells ; 

 it is, however, destitute of cells. Above this space, very narrow, slender and long 

 cells are situated which are perpendicular to the outer convex surface of the organ, and 

 extend between it and the central cavity, above referred to. These cells are spindle- 

 shaped, tapering to fine points at each end, and have elongated, oval nuclei, and 

 in consequence of their shape and position give to this part of the organ a 

 radially striped appearance. Just below the outer surface there is a granular zone 

 about 0"01 mm. mde, with spherical nuclei, but in this zone the radial structure is 

 rather obscured by the granules. The whole structure is exceedinglj^ transparent 

 and possesses — in spirit — that peculiar white colour which is so characteristic of all 

 these organs. 



c. Innervation. 



The medullary nerves found in the walls of the pyi-amidal tubes originate from fibres 

 which extend along the lower surface of the organ ; the latter form a kind of plexus in 

 that locality, which is connected with nerves belonging to the system of the spinal 

 nerves. The plexus and the branches which connect it with the spinal system are 

 modified dermal nerves. 



d. Function. 



From these facts we may conclude that these organs are composed of a gland, 

 consisting of closely packed and therefore flattened and polygonal tubes, on the lower 

 side, and a special phosphorescent apparatus above, which produces light at the volition of 

 the fish by using up or burning the secretion supplied by the gland and stored in the 

 space below. This phosphorescent apparatus is innervated from above, where a layer of 

 ganglion cells— the granular layer with the spherical nuclei — is found. 



The state of preservation of these organs is not suflaciently good to allow of a more 

 detailed description, but the whole structure is so similar to that of some other organs to 

 be described, which I was able to study by means of excellent material, that I consider 

 myself justified in referring for further details to the descriptions of the phosphorescent 

 apparatus in the suborbital organs of Oiwstomias micnpyms, and the composite ocellar 

 organs in Scopelus henoiti. 



At the first glance these organs, scattered in dense crowds over the fish, remind one 

 of the chromatophores of Cephalopods, and they are in all probability defensive arrange- 

 ments to frighten away fish of prey, which may attack them from above. Proba])ly the 

 fish, by simultaneously exciting certain groups of these organs, is able to emit light from 

 tliese areas. As the organs in difterent regions of the surface are successively incited to 



