PHOTOPHORES OF DECAPOD CRUSTACEA 329 



That all these structures in Hoplophonis are truly luminous organs was proved beyond 

 any possibility of doubt by Dr Kemp. On placing a living female specimen of 

 H. grimaldii in fresh water all the photophores emitted light, described as feebler than 

 that of Euphansia longirostris taken in numbers at the same time. This appears to be 

 the first occasion on which luminescence, apart from the production of clouds of a 

 luminous secretion, has actually been observed in any Carid. 



In the following account attention has been concentrated on the structure of some of 

 the photophores rather than on their number and position in the different species. 



(a) The pleopod photophores of Hoplophorus novae-zealandiae 

 The pleopod photophores of Hoplophorus, like those of Systellaspis dehilis (Kemp, 

 i()iob, p. 643) and S. affinis (this paper, p. 346) are situated at the distal end of the 

 coxopodite on a slight downwardly facing projection borne externally and antero- 

 laterally. Their position is well shown in the figure of Hoplophonis grimaldii given 

 by Coutiere (1905, fig. i). They are overlapped by the extensive pleura of the 

 abdominal somites, and would be unseen in lateral view if the pigment of the pleura 

 were uniform. Although I have discovered no reference to any lack of pigment in those 

 parts of the pleura immediately overlying the photophores, such as occurs in Systellaspis 

 dehilis (Kemp, 1910Z), p. 645), I have no doubt that in the species of Hoplophorus a 

 similar transparent window-like area, through which light emitted by the photophores 

 may shine, is also present. 



Pleopod photophores are present and are closely allied in structure in all three species 

 of Hoplophorus examined. They are found on all five pairs of pleopods, and similar 

 organs are found at the base of the uropods. In his 'Discovery' notes on H. grimaldii 

 Dr Kemp remarks that the pleopod photophores appear to resemble those on the 

 carapace. Actually the pleopod organs consist basically of radially arranged photogenic 

 cells, while those on the carapace show a linear grouping of very closely similar cells 

 (p. 339). Specimens of H. grimaldii and H. typtis, preserved in formalin, and pleopods 

 and other portions of H. novae-zealandiae, fixed in Duboscq, were available for ex- 

 amination, and the following description is therefore chiefly based on the better fixed 

 material aff^orded by H. novae-zealandiae. 



The organs are, as Kemp {i^ioh, p. 646) stated, closely similar in all essential respects 

 to those of Systellaspis dehilis, but show an even greater structural complexity, notably 

 in their possession of a well-developed musculature capable of moving the whole organ 

 with respect to the limb, and in the details of their innervation. The double convex 

 lens of the photophore, made up of thickened and diflFerentiated chitin, shows, like that 

 of S. dehilis, three well-defined layers (Fig. 10, l.o., l.m., Li.). Of these the middle layer 

 appears densest, showing closer striations than the inner and outer layers, but unlike 

 them it is not uniformly dense. Its greatest density is progressively reached at its 

 surfaces, contiguous with the inner and outer layers, so that additional middle layers, 

 one of which is indicated in Fig. 10 by the guide-line l.m'., may be distinguished. The 

 lens may thus be regarded as built of five layers of varying density, forming a distinct 



