ON LUMINOUS OEGANS OF FISHES. 



5 



Jruu 



I shall call " iris " (PI. I, figs. 1-4, ir). The reason thereof 

 will become clear further on. These pigment cells send out their 

 pseudopodia-like projections in three directions : the principal ones 



run perpendicularly to the axis of 

 the organ, thus forming a cover 

 over the cup (Textfig. 2, i) ; the 

 second run distad nearly parallel 

 to the axis at first and then bend 

 axiad, forming likewise a cover ex- 

 ternally to that formed by the 

 first (il) ; the third and least 



Fig. 2. Diagram showing the pigment- 

 ation of the punctate photophore of developed of all ruu proximad 



Etmoplerus. i group of horizontal pro- 

 cesses of iris, a group of external pro- and axiad along the inner surface 



cesses, iii group of internal processes, Inv • • i i i i i • 



involucre of pigment, L lens-cells, Vc of the CUp, mSldc the blood SlUUS 



vacuole. / • • «x 



{III). 



In sections these three projections are found in both con- 

 tracted and expanded states. In JS. frontimaculatus, in which 

 pigmentation is generally weaker than in lucifer, the impression is 

 very often produced that the organ is perfectly free from pigment 

 along the axis, thus allowing the light produced to pass freely 

 to the exterior (PL I, figs. 3 and 4). Johann has described and 

 figured the organ in this state, without mentioning the fully 

 expanded condition of the pigment cells. (PL I, figs. 1 and 2). 



Johann thought that the lens-cells originated in the 

 " Keimlager " and were then successively pushed distad increas- 

 ing in size on the way. The lens-cell when fully developed is 

 of a rounded or somewhat lenticular form with compact and 

 homogeneous contents readily stainable with orange-G and often 

 containing one or more vacuoles (PL I, figs. 1 and' 3, /). The 

 nucleus is usually found appressed to the proximal wall. 



