626 F. W. GAMBLE AND F. W. KEEBLE, 



be seen, but as though immersed in a clear blue stain. The 

 " chromatophores " are reduced to shrunken blobs of a 

 blackish colour, distributed under the alimentary canal, 

 along the nerve-cord, on the optic stalks, and scattered 

 through the connective-tissue networks. The " chromato- 

 phores" are separated from one another by comparatively wide 

 spaces, and are each surrounded by a delicate blue halo ; a 

 most delicate and intricate blue reticulum connects these 

 halos one with another. It is this reticulum which gives the 

 blue tint to the nocturne. The blue network is sti'ongly, 

 perhaps chiefly, developed in the muscles. The excised 

 muscle of a nocturne is of a brilliant blue colour. In speaking 

 of the prawns as seen in the daytime, we alluded to the 

 stores of chromatophoric pigment which occur in the muscles. 

 In some specimens of a faint blue colour to the naked eye, 

 the blue tint becomes invisible when viewed by the powerful 

 light concentrated by a sub-stage condenser, and in all cases 

 the tint appears much less vivid under a microscope than to 

 the unaided eye. 



The result of a large number of observations on the 

 " chromatophores " of nocturnes shows that the red and 

 yellow pigments are fully retracted, forming irregular 

 blackish masses. By reflected light the centre of each 

 '^ chromatophore " shows as a dark red mass with lighter 

 yellow patches, the whole enveloped in a blue pigment (PI. 

 36, figs. 33, 34). 



In some specimens strong reflected light reveals peculiar 

 coloured vacuoles at the " centres." The nature of these 

 " vacuoles " we have not investigated. 



During the examination the blue colour fades away from the 

 reticulum very quickly, and becomes concentrated round the 

 centres. The colourless branches of the " chromatophores " 

 may now be seen as the yellow and then the red pigments 

 flow outwards into them (PI. 36, fig. 33). By reflected light 

 the " chromatophores " now look green, with a bluer margin. 

 The further succession of events is diflficult to record, as 

 several rapid changes take place simultaneously ; but it is 



