172 THE RADIATING ORGANS OF THE DEEP SEA FISHES. 



a capillary vessel traversing this tissue but these appear to be rare. The 

 residual protoplasmatic masses and the nuclei appear attached to the strands 

 of the network, or the walls of the alveoles. The structure of this tissue is 

 pretty much the same throughout the whole region it occupies. 



The middle region (1) occupies the lower portion of the conic part of the 

 organ. Its limit towards the inner region is, as we have seen, concave and 

 smooth. The outer limit is not well defined, the middle region gradually 

 passing into the outer, which is composed of small digitate papillae lying 

 close together. The middle region is composed of cells, which, in longi- 

 tudinal, axial sections (Plate 6, Fig. 24) appear transversely arranged and 

 mostly long, slender, and spindle-shaped. On the whole this tissue takes 

 stains, particularly haematoxylin, somewhat less readily than the parts 

 below and above it. It is traversed by numerous capillary vessels. 

 Whether the cells here in the proximal part of the middle region are 

 really spindle-shaped or lamellar, overlying each other like the cells in 

 the epithelium of the human skin, could not be decided. Distally, towards 

 the papillae, the arrangement of these cells becomes less regular and the 

 cells themselves become smaller, the nuclei lying much closer together. 

 The papillae forming the outer region are composed of similar cells ; these 

 are often much curved, but also on the whole arranged paratangentially. 

 This outer region is poorer in blood vessels than the inner. 



The distal part of the cone beyond the outer region contains only a 

 few doubtful traces of cells and chiefly consists of a gelatinous substance, 

 which takes haematoxylin and some other stains pretty readily and which 

 in some sections exhibits a very strongly marked stratification, the layers 

 being slightly oblique to the outer surface. 



The structure of the radiating organs in the genus Argyropelecus was 

 first examined in A. hemigymmis by Ussow ('79, pp. 103-104, Plate 1, Fig. 5). 

 According to his description these organs of A. hcmigi/mnvs are similar in 

 appearance and arrangement to those of A. lychmis described above. Ussow 

 states that the internal tissue of the inner region is composed of glandular 

 cells supported by a scaffolding (Gerlist) of connective tissue. 



Leydig ('81, pp. 26-39, Plate 1, Fig. 5 ; Plate 1, Figs. 13, 14 ; Plate 3, Figs. 

 19, 20, Plate 4, Figs. 22-27 ; Plate 5, Figs. 28-31 ; Plate 6, Fig. 35) has de- 

 scribed these organs in the same species. So far as their arrangement and 

 appearance are concerned, this description accords with that of Ussow. The 

 anteorbital organ is innervated by branches of the nervus trigeminus, which 



