THE RADIATING ORGANS OF THE DEE? SEA FISHES. 195 



The compound organs of the first kind (Plate 10, Figs. 49, 51) are 

 spherical and have a short process directed downwards towards the outer 

 surface. They might be compared to spherical bottles with small necks 

 placed upside down. The axis of the organ is vertical, parallel to the median 

 plane of the fish. The ventral organs, that is, those belonging to the ventro- 

 thoracic row, therefore abut nearly vertically on the surface, whilst the lateral 

 ones, that is, those belonging to the anterior lateral row, are very oblique and 

 enclose but small ang^les with the surface of the fish. In the former the 

 "neck" appears cut off transversely; in the latter, obliquely. 



The pigment sheath (Plate 10, Fig. 51 p) enclosing the organ is rather 

 thin and composed of cells containing brown pigment. It surrounds all 

 parts of the organ with the exception of the terminal face of the " neck." 



As in other compound radiating organs we also find in these below the 

 pigment layer a reflecting layer. This is however not at all extensive, being 

 confined to the distal part of the neck-shaped portion, where it forms a ring 

 (Plate 10, Fig. 51 r) surrounding the " neck." This reflecting layer is com- 

 posed of highly refractive threads. 



Within the pigment sheath and, where this is developed, the reflecting 

 layer, a connective-tissue membrane is met with which entirely surrounds 

 the inner cell mass and forms a perfectly closed capsule, from which diver- 

 ticula extend inwards. 



The greater part of the interior of the proximal, spherical part of the 

 organ is occupied by large radially arranged conic cells Avhich converge 

 towards the centre of the sphere. These cells are very similar to the conic 

 elements in the inner region of the compound organs of ChauUodus harhatus 

 and like them consist of a long, proximal, finely granular part (ph) not 

 readily stainable, and a short, distal part (pt) showing great aflinity to 

 haematoxylin. The nucleus is remarkably small and situated in the distal 

 staining part of the cell. These cells are divided from each other by fine 

 connective-tissue membranes extending from the outer connective-tissue 

 capsule radially inward towards the centre. In these membranes small 

 radial blood vessels (b) can be made out. 



The "neck" of the organ (Plate 10, Fig. 51 cy) above referred to is a 

 stout cylinder, circular in transverse section, tlie axis of which coincides with 

 the axis of the whole organ. This cylinder is surrounded by an extensive 

 annular cavity (s) dividing it from the connective-tissue capsule forming the 

 innermost layer of the outer covering of the organ. The outer, distal, ter- 



