ON LUMINOUS ORGANS OF FISHES. 13 



mine. The latter is fouDcl well preserved only in specimens* 

 fixed with Zenker's fluid, while in those which were treated 

 like Gatti's with formalin or formalin-sublimate, it has entirely 

 disappeared, the remaining cytoplasm forming a network that ap- 

 pears exactly like that figured by him. Brauer's description of 

 the " Drüsenzellen " of Polyipnus, Slernoptyx and Argyropelecus 

 agrees with what I have found in JIaurolicus, the only differ- 

 ence lying in the absence of any regular arrangement into groups 

 found in those three genera. Mangold, like other authors, has 

 fallen into a mistake in saying that the " Drüsenkörper " of the 

 inner part is histologically indistinguishable from that of the 

 outer. On careful comparison, I have found a dijßPerence between 

 the photogenic gland-cells of the outer section and those of the 

 inner, the difference consisting in the different relative quantity 

 of the secretion product and the cytoplasmic portion. In the 

 cells of the outer section (PL I, fig. 6) the fat-drops are large and 

 numerous, occupying almost the whole interior of the cell, while 

 in those of the inner section (fig. 5) they are few and minute, 

 there being a great preponderance of the cyptoplasmic matter. 



The meaning of Mangold's " Drüsenkappe " (Textfig. 4, L) 

 is a mooted point. He emphasized its glandular nature, and 

 concluded that Gatti's unhesitating decision as lens was 

 erroneous. That body lies at the distal border of the photogenic 

 body, completely spanning over the aj)erture of the organ. 

 In vertical sections through the layer one finds the cells 

 arranged in rod-like groups at right angles to its surface (PI. 

 I, fig. 8, /). Mangold stated that the arrangement of the 

 " Leuchtdrüsen " reminds one somewhat of the sublingual gland. 



"These belong to Mr. Mokiwaki's collection. 



