188 THE RADIATING ORGANS OF THE DEEP SEA FISHES. 



the distal highly stainable terminal part of each cell one rather small nucleus 

 (nu) is situated. 



The middle region (Plate 9, Fig. 45 m) occupies the distal sector of the 

 proximal spherical part of the organ and the proximal portion of the distal 

 paraboloidal part. The proximal limit is conic, the distal limit very regularly 

 convex. The cells occupying the space between these limits (1) are well 

 defined and polyedric in shape. The distal ones are small. From here they 

 increase in size inwardly, the innermost ones being four to five times as large 

 as the outermost ones. The protoplasm of these cells is homogeneous, not 

 granular, and hardly stainable with haematoxylin. It shows a great affinity 

 to picric acid and the whole cell mass of this region appears bright yellow 

 in sections stained with picric acid-haemotoxylin. The nucleus is nearly 

 spherical and larger in the large cells than in the small. 



The distal limit of the outer region is nearly a plane vertical to the axis 

 of the organ, and so, its inner limit being concave and some distance away, 

 the outer region (Plate 9, Fig. 45 o) has the shape of a thick plane concave 

 lens. From the mass of connective tissue which abuts distally on the outer 

 region, septa, nearly vertical to the limiting surface and parallel to the axis 

 of the organ, extend inward, dividing the outer region into prismatic facets 

 rounded off distally. These facets are occupied by small elongated cells, 

 the protoplasm of which behaves towards stains in a similar manner as the 

 protoplasm of the cells of the middle region. 



The compound radiating organs of Chauliodus were first studied in 0. 

 sfoam by Leuckart ('64, pp. 153-155). According to his description these 

 organs of C. sloani are similar to those of C. barhatiis. Leuckart chiefly 

 studied the branchiostegal radiating organs (1. c, p. 154). These are 

 cylinders, 1 mm. long and 500 yu broad. Their distal portion is occupied by 

 a structure Leuckart considers as a lens. From the proximal face of this a 

 conic protuberance arises, penetrating some distance into the inner cell 

 mass ; as mentioned above such a cone is also observed in C. barhatiis. The 

 reflecting layer consists of hexagonal pavement cells occupied by numerous 

 crystals. In the outer part of the distal mass, that is, in the " lens," Leuckart 

 claims to have seen fibres, whilst the inner part, and the proximal cone are 

 composed of closely packed rods 5 /a thick radiating from the apex of the 

 cone. The substance composing these rods is highly refractive. No fibres 

 or rods of this description occur in the middle and outer regions, which cor- 

 respond to Leuckart's " lens," in the compound organs of C. barbatus. The 



