()50 ox THE PIIOTOPHORKS OF DECAPOD CRUSTACEA. [Apr. 19, 



inidwater organisms while being hauled, and there is reason to 

 ])elieve that errors arising from this source exist in many of the 

 instances in which animals bearing photophores hav^e been 

 recorded from the bottom. 



Many of the higher marine animals live on the sea-floor at 

 depths to which no ray of sunlight can ever penetrate, and, though 

 they possess well-developed eyes, are themselves, for the most 

 part, without any special illuminating appaiatus. That light 

 exists at these depths seems almost cei-tain. It is probably fairly 

 plentiful in regions thickly populated by Cffilenterates, and the 

 excretions of numerous animals of a more highly organised nature 

 have been found to be brilliantly phosphorescent. The restriction 

 of photophores to species living in midwater seems only explicable 

 on the theory that there is a comparatively plentiful supply of 

 light on the bottom itself. 



The sections of the photophores were made by the pai-affln 

 method in the laboratories of Trinity College, Dublin. Decalcifi- 

 cation was not attempted, for it was found that the cuticle was 

 sufficiently soft without it, this, perhaps, being due to the fact 

 that the specimens wei^e preserved in formalin. 



In conclusion, I wish to acknowledge my indebtedness to 

 Dr. W. T. Caiman for much useful help and criticism, and to 

 J)r. H. H. Dixon for his valuable assistance and advice in the 

 preparation of the sections and micro photographs. 



EXPLANATIOX OF THE PLATES. 



Plate LII. 

 The figures on this Plate are reproduced from micro-photographs. 



Acantheplii/ra dehilis A. M.-Edw. 



Fig. 1. A longitudinal section of a photo])li()re from the protopodite of the pleopud. 

 X 185. (Compare fig. 1, Pi. LI V.) 



2. A transverse section of the pliotopliore bcliind the base of tlie lust i)air of 



legs. X 133. 



Plate LIIL 

 The figures on tliis Plate are rei)roilui-('d from micro-i)hotographs. 



Acanthephi/ra dehilis A. M.-Edw. 



Fig. 1. A transverse section of the telson near the apex, passing through the median 

 dorsal patcli of blue pignn'ut. The section shows the regular arrangement 

 of nuclei l)el()W this area and also the bases of two spines cut trans- 

 versely. X V>3. 



Sergestes challengcri Hansen. 



Fig. 2. A median pliotopliore from the thoracic sternum, cut transversely. X 320. 



3. Part of the peiuiltimati? joint of the second maxillipcde, cut longitudinally, 



showing a jjhotophore in transverse section. X 2t7. (Compare fig. 3, 

 I'l. I>IV.| 

 1. The photojihore at the ])ase of the exopod of the first inaxillipede in trans- 

 verse .section. X 30U. 



