ON LUMINOUS ORGANS OF FISHES. 23 



POSTSCRIPT. 



While the furet^joing was in press, I was fortunate enough to get a 

 copy of Handrick's work '^ Zur Kenntnis des Nervensystems und der Leucht- 

 organe von ArgyropeJecus hemigymmis " (Zoologica Bd. XXIII, Heft 32, 

 1901), which I was not able to consult before. In this work Handrick 

 mentions the presence of two forms of glandular cells in the luminous 

 organs of Argyropelecus, viz., (1) those situated principally near the reflector 

 layer, which have sickle-shaped mass of protoplasm attached to the cell-wall 

 and usually contain vacuoles (Sekreträurae), and (2) those found apart from 

 the reflector, without any localized mass of protoplasm and rarely 

 with vacuoles. Both these cells contain in the reticulated protoplasm 

 " verhältnismässig grosse, stark lichtbrechende Körperchen ", noted before 

 by Brandes. In my opinion, the two forms of the cells mentioned by 

 Handrick correspond to the two forms of photogenic cells described by 

 me in this paper from MauroUcufi. Further, the refractive "Körperchen" 

 found by him in the cells can not be anything else than what I have 

 called fat-drops. Then, the only essential difference in the histological 

 structure of the luminous organs of Maurolicus and Argyropelecus seems 

 to consist in the relative distribution of the two kinds of photogenic 

 cells, viz., while in Argyropelecus both kinds appear to occur in the outer 

 funnel-like as well as in the inner bulbous section of the organ, the 

 first near the reflector and the second in a more internal position, the 

 same in Maurolicus are found separately in the two sections, in that the 

 first and the second fill up respectively the bulbous and the outer funnel- 

 like section. I may call attention to the fact that in Maurolicus, the 

 two forms of the cells are connected by intermediate ones, so that there 

 can be no doubt that all the cells in question are of the Fame origin, 

 showing differentiation in the quantities of the protoplasm retained and 

 of the fat-drops contained in the cell body. 



May 14, 1910. 



