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 longt- 
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. hemigymnus by Ussow (79, pp. 103-104, Plate 1, Fig. 95). 
According to his description these organs of A. hemigymnus are similar in 
appearance and arrangement to those of A. lychnus described above. Ussow 
states that the internal tissue of the inner region is composed of glandular 
cells supported by a scaffolding (Geriist) 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 
Be 
