644 MU. STANLEY KKMI' ox THE [Apr. 19, 



np a certain nniouiit of yellow colour (due to the picric acid in 

 the stain), it seems probable that it is formed of u more strongly 

 chitinised material. 1'he cuticle is thi-own in folds on either side 

 of the lens. It is possible that by this structure a limited amount 

 of movement is permitted to the photophure, but no trace of a 

 controlling muscular appai-atus could be found. 



Inside the lens there is a series of very large elongate cells 

 which radiate from a well-defined centre to its inner surface. 

 They measure fiom -08 to '10 nun. in length ; twenty are usually 

 visible in a median longitudinal section, consequently at lea.st 

 three hundred n)ust occm- in the whole organ. The proximal 

 portions of these cells ap])ear to be wholly devoid of protoplasmal 

 contents. The nuclei* are very regular in shape and, as in the 

 first cellular layer of Sergestes, lie close up against the lens. The 

 outer end of each is evenly roun<led, and a band of cytoplasm 

 may sometimes be seen between it and the lens; the inner end is 

 squaiely truncate. The nuclei difter cuiiously in size, for in all 

 the sections obtained the length is proportional to the distance 

 from the centie of the lens. This results, in efiect, in the fornja- 

 tion of an additional lens, concavo-convex and built entirely of 

 nuclei, which is placed in)mediately behind that formed from the 

 cuticular layer. There can be little doubt that such a pi-ovision 

 as this must have a marked efiect on the optical qualities of the 

 apparatus. 



The centi'al ])nrt of the organ is occupied by a numl)er of 

 minute highly refractive granules which are massed together in 

 a conical shape round the extremity of the nerve-bundle. These 

 granules are quite colourless in every section obtained ; c-irmine, 

 picric acid, and luematoxylin are all ecpially ineftectual in staining 

 them. The nerve-strand leads straight doAvn the pleopod to the 

 photophore, and, as may be seen from the figures, it expands into 

 a number of ramifying filaments before it convei'ges to the 

 granular cone. 



Numerous cells with large nuclei are irregulaily disposed rotmd 

 the inside of the })hotophore. It is possible that the.se Avere 

 pigmented when the animal was living, and served as a screen to 

 ])revent light })enetiating inwards, but no continuation of this 

 was obtained. 



In a freshly cuight s])ecimen of Acanthephyra debilis a dark 

 violet-blue streak is easily seen on each side of the inner wall of 

 the carapace immediately behind the last pair of thoracic legs. 

 From the structme which these organs possess it is evident that 

 they also are photophores, although they are much less highly 

 speciali.sed than those at the base of the pleojjods. 



In a transver.se .section (PI. LII. fig. 2) the lens, Avhich is dark 

 blue in fre.sh material, is seen to be merely a slight thickening 

 of the cuticle, and the densely .staining central layer is entirely 

 absent. The epithelial cells are greatly elongated, as in the 



* ThcYc can be no donbt thHt thpscKoflies are nuclei, for by theiiijc ot hjcinatoxylin 

 rhi'onuisonu's wvrc dcinoii.'itratcd in them. 



