182 THE RADIATING ORGANS OF THE DEEP SEA FISHES. 



Myctophum aurolaternatnm Gnrman. 



Plate 5, Figs. 21-23. 



This species has been described b}^ Garman ('99, p. 254, PLate 55, Fig. 3). 

 His statements concerning the distribution of the radiating organs agree with 

 my observations, but his figure ('99, Plate 55, Fig. 3) differs in several 

 respects from what I find in the specimen examined. 



The radiating organs are for the most part nearly equal in size about 

 600 fx in diameter. They are provided with reflectors, lustrous, and there- 

 fore, although so small in size, quite conspicuous. 



There are on each side 3 mandibular (Plate 5, Figs. 21, 22 ma), — these are 

 mentioned by Garman ('99, p. 265), but not represented in his figure ('99, 

 Plate 55, Fig. 3), — 4 branchiostegal, 2 opercular (op), — the lower one, 

 which is smaller than the upper one, is not represented in Garman's figure 

 ('99, Plate 55, Fig. 3), — 3 pectoral (pe) forming an arc just behind the 

 gill slit, 5 ventrothoracic (vt), over the last of these 1 anterior lateral (al), 

 4 ventromedials (ve), 3 mediolaterals (ml) forming an oblique row, 10 

 anterior ventroanal (va), 1 posterior lateral (pi), over the last one of the 

 former 6 posterior ventroanal (vp) — according to Garman's figure ('99, 

 Plate 55, Fig. 3) 7, — and 2 ventrocaudal radiating organs (vc) at the base 

 of the tail. 



All the organs examined appear to have the same structure. Viewed 

 from the surface each appears as a lustrous spot enclosed above and at the 

 sides by a dark strip, which has the shape of a horseshoe open below. 

 Each radiating organ of the body lies between two scales. The outer one 

 which covers it (Plate 5, Fig. 23 ss) is convex and possesses near the centre an 

 ri-shaped thickening (t) produced by a local accumulation of calcareous 

 laminae, which make the scale very brittle. On treatment with acid the 

 thickening disappears. The horseshoe-shaped pigment stripe mentioned 

 above is attached to the inner side of this scale. An axial section of the 

 organ vertical to the medial plane of the fish passes through the apex of 

 the horseshoe (p). The lower scale (si) is concave; on its inner side a 

 continuous layer of pigment (pp) is observed. The lenticular space be- 

 tween the convex outer and the concave inner scale is for the most part 

 occupied by connective tissue (c). This is composed of a ground substance 

 traversed by slender, elongated cells which are somewhat irregularly curved. 



