130 



HISTOLOGY 



The chief portion of this organ consists of a nearly spherical mass 

 of tissue which is not moved by muscles, as has been asserted by some 



authorities, but lies loosely 

 embedded in the tissues 

 of the body wall and 

 bounded distally by the 

 cuticle. The proximal 

 bounding layer is con- 

 nective tissue, from its 

 appearance, and is devel- 

 oped to act as the re- 

 flector by the plate-like 

 arrangement of its lamellae, 

 which are thin, and placed 

 in a parallel cup-shaped 

 layer that embraces the 

 rest of the organ on its 

 inner end. There are 

 but few nuclei scattered 

 through this layer. This 

 reflector is thin, and on 

 its outer or proximal 



FIG. 119. Light-organ of N yctiphanes Noruegica. lu.c., 

 luminous cells; c., cornea; /., lens; ref., reflector; fi., fi- 

 brillar mass. (After VALLENTIN and CUNNINGHAM.) 



surface it is covered with 

 a layer of red pigment 

 cells. 



The next layer distad is a columnar layer of thick, heavy cells that 

 form a cup-like structure lying in and touching intimately, the reflector. 

 The nuclei of these cells lie mostly distad in the layer, although some few 

 are found proximally. This is apparently because the layer is not en- 

 tirely single, but partially stratified in some places. These large cells show 

 a cytoplasm that is full of some granular secretion, and they are probably 

 the gland cells which secrete the light substance or luciferase. Con- 

 siderable difference of opinion exists as to just which cells were the 

 actual source of the light, and it is possible that a light substance may 

 be produced in this layer and then discharged against the reflector or, 

 more probably, into the inner fibrillar mass, to be there oxidized and 

 made to shine. 



This peculiar mass lies in the cup-like embrace of the last layer de- 

 scribed, the gland cells. It is made up of several bundles crossing each 

 other at an angle, and its outer (proximal) layer forms a series of shorter 

 radial rods. Nuclei are very scarce in connection with it, and where 

 found on its edge evidently belong to other tissues. Placed above this 

 mass distally and overlapping the glandular layer is a single, very per- 



