PHOTOPHORES OF DECAPOD CRUSTACEA 375 



occurs a layer of cells containing (ammonium?) urate granules which is said to con- 

 stitute a reflector. Briefly, as a result of morphological and physiological investigations, 

 Lund found that " photogenesis is incident upon the utilization of a nitrogenous 

 compound — the photogenic granules — giving staining reactions like those of lecithin 

 and different from those of the true fats, and that this nitrogenous compound appears 

 at least in part at the end of the process in the form of a nitrogenous waste product. 

 This crystalline substance appears from its reactions to be allied to or identical with 

 some of the split products of nucleic acid." Lund also discovered that the minutely 

 crystalline waste product accumulates in the cells of the dorsal layer, and that no direct 

 transformation of photogenic cells into dorsal "urate" cells, by their becoming loaded 

 with the waste product, takes place. He gives dark-ground photographs of the organs 

 (191 1, pi. 2, figs. 5, 6) which may be compared with Plate XXV, figs. 4 and 5 of this paper. 



It will be readily apparent from the foregoing that a similar phenomenon almost 

 certainly takes place in the photophores of S. affitiis under discussion. Here, however, 

 the waste product appears, from the morphological evidence at least, to be derived 

 from the katabolism of the nucleus itself, and not from the breakdown of photogenic 

 granules around it. But the increase in size of the radially arranged segments after 

 the total disappearance of the nuclei concerned is wevy peculiar and not in accordance 

 with the general conception of nuclear control of tissue activity, and suggests the 

 possibility that waste material resulting from metabolism in other parts of the body 

 may accumulate in these organs. 



Such a consideration raises the doubt that the organs may not actually be luminous, 

 but serve only as part of an accessory excretory system, or at any rate that luminescence 

 may only be a purely incidental accompaniment of such a system. (It is of interest 

 that in the larva of the Tipulid Bolitophila liiminosa of New Zealand caves the distal 

 ends of the Malpighian tubules are modified as luminous organs, and are associated 

 with a layer of tissue containing reflecting granules (Wheeler and WiUiams, 1915).) 

 This view, it is true, may receive some support from the observation (p. 360) that the 

 granular deposits occur on the outer and superficial side of the organs, where they 

 would, instead of acting as a reflector, only serve to mask any emission of light by the 

 organs. On the other hand, organs of a very similar structure in Hoplophorus (p. 337) 

 have been observed by Dr Kemp actually to luminesce, and, furthermore, the uropod 

 organs of Systellaspis affinis, which from a comparison with the pleopod photophores of 

 Hoplophorus can be nothing else than photophores, also possess a basal granular deposit 

 of precisely similar opaque white substance. 



I suggest, then, if only tentatively, that in these organs of Systellaspis affinis reactions 

 resulting in the emission of light take place in the neighbourhood of the nucleus and 

 involve its degeneration, and that the prominent granular masses are, as in the Lampy- 

 rids, stored waste products resulting from these reactions. What part is played in these 

 processes by luciferin and luciferase must be left to future workers having the oppor- 

 tunity of studying freshly caught material. 



The photophores of Hoplophorus such as those behind the bases of the fifth thoracic 



