PHOTOPHORES OF DECAPOD CRUSTACEA 



367 



n.chit.ep.), but behind the photogenic cells are situated large flattened and somewhat 

 rectangular nuclei which I have called on account of their position "reflector nuclei" 



(Fig. 30, n.r.). 



Lying close against the lower ends of the photogenic nuclei occurs a slight granular 

 deposit (Fig. 30, gr.). It appears a light golden yellow by transmitted light, but is 

 almost invisible by reflected light, and is apparently of a different nature from the 

 white opaque substance so prominent in the photophores of Systellaspis affiuis. It 

 provides the only instance known to me of granules situated at the distal end of cells of 

 this type, for it will be recalled that elsewhere any granules associated with similar 

 photogenic cells are basally situated and are intimately related to the nerve fibres 

 supplying the organ. 



n.chitep. 



Fig. 30. One of the smaller carapace photophores of Systellaspis debilis; a, in vertical section, the external 

 surface being to the right; b, in surface view. The haemocoele is indicated by mechanical stippling, gr. 

 granules; ii.chit.ep. nucleus of chitogenous epithelium; n.phot.c. nucleus of photogenic cell; n.r. reflector 

 nucleus ; phot.c.cl.a. clear area of photogenic cell. 



The contrast between the carapace photophores of S. affinis and those of S. debilis 

 adds still further to the divergence of these two species with regard to their photo- 

 phores. 



{e) The photophores on the ielson 



The photophores on the telson of S. debilis consist of two pigmented spots placed 

 dorsally in the median line. The anterior spot is situated not far behind the base of the 

 telson, just between the posterior points of attachment of the pair of telson extensor 

 muscles, and the posterior rather smaller spot is placed near the apex at the level of the 

 anterior limit of the posterior armature of six pairs of articulated lateral spines (cf. 

 Kemp, 1906, pi. ii, fig. 7). Ahhough occupying a dorsal position rarely encountered in 



