THE KADIATING ORGANS OF THE DEEP SEA FISHES. 171 



separated by a clearly marked constriction (C). The proximal oval part has 

 in the single organs a circular transverse section throughout; in the joined 

 organs it is not so regular. The distal funnel shaped part is in life probably 

 a rotation paraboloid, but on account of shrinkage appears somewhat irreg- 

 ular in the sections (Fig. 24). In accordance with the smallness of the 

 angle enclosed between the axis of the organ and the surface of the fish, 

 the funnel abuts very obliquely on the latter ; it is long on the inner, and 

 very short on the outer face, a very oblique truncated cone with bulging 

 parabolic sides. 



The whole organ with the exception of the funnel mouth, which is closed 

 by a transparent membrane, is surrounded by a thin layer of cells containing 

 a dark brow^n pigment. These form an outer pigment sheath (p). Inside 

 this lies another sheath composed of colorless, highly refractive fibres. 

 This (r) is exceedingly thick at the proximal end of the inner, oval part of 

 the organ and gradually thins out from here to the margin of the funnel. 

 It is most highly developed in the joined ventro thoracic organs, where it 

 forms a continuous mass. The fibres composing this layer are parallel, 

 pretty stout, lie close together, and extend longitudinally from the proximal 

 apex of the elliptical part to the distal margin of the funnel. In life these 

 fibres probably follow the curvature of the layer which they form, but are 

 not otherwise bent. In sections (Fig. 24) they often form zigzag lines in the 

 distal thin part of the reflecting layer (B). This also is probably attributable 

 to shrinkage. 



In the tissue occupying the proximal and central part of the interior 

 space surrounded by the fibrous layer three regions can be distinguished : 

 an inner (g), a middle (1), and an outer (s). The limits between these regions 

 are well defined. The inner reo-ion extends to the constriction between the 



o 



oval and conic part of the organ and there ends with a slightly convex sin-- 

 face vertical to the axis. In the joined organs, particularly in the ventro- 

 thoracics, the inner regions of adjacent organs coalesce to form extensive 

 cellular masses surrounded by common fibre and pigment sheaths. 



The tissue occupying the inner region (g) has in all sections, whatever 

 their direction may be, an alveolar or reticulate appearance ; in the alveoles 

 or meshes residual masses of protoplasm and small spherical nuclei, both 

 readily staining with haematoxylin, are clearly visible. Very rarely a slight 

 indication of an arrangement of the meshes of this network in rows is met 

 with. The meshes or alveoles are about 20 /a wide. Occasionally one sees 



