THE RADIATING ORGANS OF THE DEEP SEA FISHES. 197 



on the hinder part of the body have the same structure as the compound 

 organs of ChauUodiia harbatus described above. It is therefore not necessary 

 to give a detailed account of them. 



(■2)TIIR FISHES WITH liADIATING DISCS. 

 BaSSOZetUS naSUS Gannan. 



Plate 4, Fins. llir. 



This species has been described by Garinan ('00, pp. 150, 30 J, Plates 77, 78). 

 Its head shows a number of deep depressions (Plate 4, Fig. 14). On remov- 

 ing- the semitransparent skin from it a number of subdermal, clearly defined, 

 white, somewhat elongated, rhombical patches 1-3 mm. long are exposed to 

 view. A stout nerve filn-e leads to each one of tliese. There are on each 

 side of the head 3 maxillary, 6 orbital, 3 ethmoidal, 3 frontal, 5 occipito- 

 parietal, 5 mandibular, and 4 opercular patches of tliis kind. Tiiese 1 desig- 

 nate as radiating discs. 



Each radiating disc appears as a thickening of the membrane wliich lies 

 close to the bone and can be easily withdrawn therefrom. The basal part 

 of the thickening, that is, the part lying next tlie bone, contains pigment 

 cells, which form a pretty continuous basal layer (Plate 4, Figs. ir)-17 p). 

 Numerous blood vessels (Plate 4, Fig. 17 b), enter the thickening from all 

 siiles and form a dense capillary reticulaticui in its central part, just Ijelow 

 the up2:)er surface. The stout nerve (Figs. 10-17 n), mentioned al)Ove, 

 which I desiscnate as the main disc nerve, also enters the thickenincr at its 

 margin. Without appreciably diminishing in width it extends through the 

 basal part of the thickening to its centre where it abruptly divides into a 

 number of fine branches. These lie in a paratangential plane and radiate 

 in all directions in it. Repeatedly ramifying they approach the margin of 

 the thickening wlieri' they become obscured by the pigment cells which 

 form a dense reticulation (Figs. 15, 16 p), lying at a rather lower level than 

 the nerves. No peculiar histological differentiation could be made out 

 within the disc. In transverse sections (Fig. 17) one merely sees faint 

 paratangential lines and elongated nuclei also disposed paratangentially. 

 Thus it appears to be composed of paratangentially extended plate-like or 

 fibrous cells overlying each other in several layers. Between these cells the 

 nerve branches extend. Judging from the appearance of the whole organ 



