PHOTOPHORES OF DECAPOD CRUSTACEA 373 



Careful consideration of freshly caught material is necessary in order to determine 

 whether the characteristic clear areas of the photogenic cells of the pleopod and other 

 photophores of the Hoplophoridae are merely products of the methods of fixation and 

 preservation employed, or whether they exist in the living animal, having only fluid 

 contents. Terao (1917) has suggested, as a resuh of his experience with the photophores 

 of Sergestes Iticens, where the photogenic cells readily disintegrated, that the clear areas 

 arise as fixation effects, or even from the natural processes in the photophore by the 

 consumption of the secreted products of the photogenic cells. He says : " Thus, it seems 

 to me not unlikely that what Kemp has given as photogenous cells in his representation 

 of the photophores of Acanthephyra debilis are not cells at all, but empty spaces left 

 behind by photogenous cells which had disappeared. The lines taken by him for the 

 walls of photogenous cells were probably nothing else than connective strands, while 

 the mass of minute and highly refractive granules at the end of the nerve bundle 

 reaching the photogenic layer may simply be the remnants of the disintegration pro- 

 ducts of photogenic cells." I do not agree with the view expressed by Terao, for the 

 segmentation of the granular mass in accordance with the number of photogenic cells 

 in Hoplophonis novae-zealandiae, and the similarity of the granular mass to the basal 

 caps of the carapace photophores (p. 342), which are again in close relation with the 

 photophore nerve fibres, seems to indicate that it is an intrinsic and essential part of 

 the organ. 



It is possible that in life the photogenic cells contain a substance secreted by the 

 distal contents of the cells and which is not apparent in the preserved material. That 

 this substance may be expected to be a luciferase is suggested by the work of Harvey 

 (1919), who finds that in Cypridina hilgendorfii the luciferase is only present in the 

 photogenic cells, while luciferin is abundant and is found in various tissues of the body. 

 In view of the small individual size of the photophores, the production in them of a 

 luciferase only required in small quantity and only very slowly consumed during the 

 process of light production would be an economical arrangement. 



If this suggestion is correct then two questions remain to be answered. The first 

 concerns the mode of transport of luciferin to the photogenic cells, and it can only be 

 suggested that, carried by the body fluid, it reaches the cells either by osmosis or by 

 simple diffusion. The second question concerns the details of the innervation of the 

 photogenic cells. It will be recalled that the nerve fibres in these organs impinge on a 

 granular cone, which may or may not be segmented, and which is in contact with the 

 basal ends of the photogenic cells (p. 331). The nucleus and small amount of cytoplasm 

 of the cells is distal and remote from the granular cone, and it is not clear what part 

 nerve impulses might play in their activity. In any event, if they produce luciferase, 

 which is apparently of the nature of a catalyst and is only very slowly consumed during 

 photogenic reactions, then variations in nervous stimuli affecting the secretory activity 

 of this zone could hardly be expected to control the luminescence of the organ. Harvey 

 (191 9) points out that i g. of a luciferase will accelerate the oxidation of 10,000 g. of 

 luciferin. 



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