276 THE VOYAGE OF H.M.S. CHALLENGER. 



bounded interiorly by the connective tissue pigment-bearing layer, no doubt of dermic 

 origin, as in the organs of the Scopclidae. 



The most important point in which the organs of Ipnops appear to differ from the 

 group of allied organs in fishes generally as yet described seems to be the nature of the 

 rod layer. The rods in Ipnops are hexagonal in section and show no tendency to 

 taper to fine filaments at either end. At the free end directed towards the exterior and 

 the light, they are capped by very definite and distinct hexagonal nucleated cells, which 

 easily become detached from them as a continuous membranous sheet. At their 

 opposite extremities the rods abut on the concave surfaces of the hexagonal pigment- 

 cells by broad hexagonal bases, as may be seen by viewing their ends through thc^ 

 substance of these cells. No arrangement of rods such as this has been described in 

 any phosphorescent or allied organ from a fish. The absence of tapetal plates is a 

 matter of less importance. They seem to be represented by the hexagonal pigmented 

 cells. The brown pigmented network described as traversing the basal regions of the 

 rod layer in Ipnops, and sending up fine branches which ramifj- at its surface, 

 apparently corresponds with the " Fachwerk " traversing the grey body in the eye-like 

 bodies of other fishes (Leydig, loc. cit., p. 68). This network is the only structure which 

 I have found in Ipnops which would in any way correspond with the structures figured by 

 Ussow as ganglion cells in what he terms the retina of the eye-Hke bodies of ChavModus 

 sloani (Ussow, loc. cit., Ta£ ii. fig. 7). 



