THE RADIATING ORGANS OF THE DEEP SEA FISHES. 107 



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

 organs of Chaidiodus harhatus described above. It is therefore not necessary 

 to give a detailed account of them. 



(2) THE FISHES WITH RADIATING DISCS. 

 BasSOZetUS naSUS Garman. 



Plate 4, Figs. 14-17. 



This species has been described by Garman ('99, pp. 159, 361, 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 fibre leads to each one of these. 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 this kind. These I desig- 

 nate as radiating discs. 



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

 close to the bone and can be easily withdrawn therefrom.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

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

 cells, which form a pretty continuous basal layer (Plate 4, Figs. 15-17 p). 

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

 sides and form a dense capillary reticulation in its central part, just below 

 the upper surface. The stout nerve (Figs. 15-17 n), mentioned above, 

 which I designate as the main disc nerve, also enters the thickening 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 where 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 



