184 THE RADIATING ORGANS OF THE DEEP SEA EISHES. 



stegal, 8 guttural (Plate 8, Fig. 39 g), 19 ventrothoracic (Figs. 38, 39 vt), 22 

 ventromedial (Figs. 38, 39 ve), 11 ventroanal (Figs. 38, 39 a), 17 ante- 

 rior lateral (Figs. 38, 39 al), and 22 medial lateral (Figs. 38, 39 ml). 



The simple radiating organs without pigment sheath are not in a partic- 

 ularly good state of preservation. So far as they could be made out, their 

 structure corresponds with the same organs of ChauUodtts sloani described by 

 Chiarini ('99, pp. 16, 17). They are spherical or oval, enclosed in a capsule 

 of coimective tissue and composed of a layer of superficial, radial, cylin- 

 drical elements surrounding a group of central polyedrical cells. 



The simple radiating organs with pigment sheath (Plate 9, Figs. 43, 44) 

 have an oval (Fig. 43) or irregular (Fig. 44) shape. They seem, however, 

 always to be elongated in the direction of their axis. The angle between 

 the axis and the part of the surface of the fish where they are situated is 

 very variable. It may be 90°, the organ then being vertical to the surface 

 (Fig. 43), or it may be smaller, sometimes so small that the axis of the 

 organ is nearly parallel to tlie surface of the fish (Fig. 44). It appears that 

 this angle is correlated to the shape of the organs, the regularly oval ones 

 being usually vertical to the surface, the irregular ones inclined to it ; and 

 it seems that the organs are the more irregular the more obliquely they are 

 situated. These organs are not, as is generally the case, imbedded entirely 

 in the body of the fish, but protrude considerably over the surface, forming 

 rather conspicuous rounded protuberances (Plate 9, Figs. 43, 44). They 

 are covered distally by a layer of considerable thickness (Plate 9, Figs. 43, 

 44 h) which appears structureless and transparent in the sections. Laterally 

 and proximally they are enclosed in a pigment sheath (p). In the regu- 

 larly oval organs of this kind the axis of which is vertical to the surface 

 (Fig. 43) the pigment sheath extends only over the part of the organ 

 imbedded in the body of the fish. In the irregular ones (Fig. 44) with 

 oblique axis it covers also the proximal portion of the protruding part. 

 The pigment sheath is thickest at the proximal apex of the organ and 

 gradually thins out towards the margin. Its distal orifice is of considerable 

 extent, and occupies about a third of the whole surface. In this a fine 

 connective-tissue membrane (Plate 9, Figs. 43, 44 c) is extended which here 

 replaces the pigment sheath. In this thin layer which separates the radiat- 

 ing cell mass proper from the structureless outer covering mentioned above, 

 nuclei, appearing paratangentially elongated in axial sections of the organ, 

 are observed. The interior of the organ is occupied by a mass of poly- 



