322 DISCOVERY REPORTS 



Investing the organ on its inner side and separating it from the blood space behind 

 it is a thin layer of connective tissue, occasional strands of which traverse the blood 

 space. 



No nerve has been observed actually in connexion with the photophore, although in 

 some sections a small nerve was seen to terminate rather abruptly in its neighbourhood. 

 It may be possible that this is the photophore nerve, the intervening portion not being 

 readily apparent with the methods employed. 



The organ just described is clearly very different from those in the branchial chamber 

 described by Hansen (1903) and Kemp (1910Z)) which possess a prominent nerve supply 

 and are identical in structure with those found elsewhere in the body. In view of the 

 fact that the branchial chamber photophores are in structure precisely the same as those 

 scattered profusely over the surface of the body, it may be possible that those species of 

 Sergestes having the longitudinal streak in the branchial chamber have also photophores 

 of similar structure in other parts of the body. Although search has been made this has 

 not been confirmed. No colour was retained by these specimens after preservation for a 

 considerable time, and such structures, presumably pigmented in life, would not be 

 readily apparent. 



The occurrence of this supposed photophore in the branchial chamber in S. corni- 

 culiim, S. diapontius, S. sargassi, and S. edwardsii may prove to have some taxonomic 

 importance. After mentioning the "complex photophores" of S. challengeri and its 

 allies, and the "simple subcuticular bodies" of S. robustus and its close relatives, 

 Burkenroad (1937, P- 3 17) says : " Superficial and presumably ectodermal or mesodermal 

 photophores of these types, which have no structural relation at all to the endodermal 

 organs of Pesta, seem to be absent in all the species in which the latter occur." The 

 branchial chamber organ of S. corniculnm and its allies, of apparently ectodermal origin, 

 has no relation to the organs of Pesta, and if it should be proved to be truly luminous its 

 presence would call for modification of the above-quoted statement by Burkenroad. 



In considering the significance of photophores in the branchial chamber roof, whether 

 several and complex, as in S. c/iollefigeri, or single and relatively simple, as in S. 

 cornictdum, the position of the organs of Pesta, also inevitably illuminating the branchial 

 chamber, must not be lost sight of. Whatever may be the various uses subserved by 

 luminous organs in the Decapoda, the presence of these structures emitting light on to 

 the gills adds still further complexities to any speculation. 



IV. CARIDEA: PANDALIDAE 

 Parapandalus richardi (Coutiere) 

 In examining freshly caught specimens of P. richardi (Coutiere, 1905, p. 18, as 

 Stylopmidahis) on board the 'Discovery', Dr Kemp noted two groups of structures 

 which in his opinion may possibly be luminous organs. He says in his notes made at 

 the time: "Pleopods colourless, but with a deep red spot at base of endopod in first 

 three pairs only", and also: "The patches of red pigment on the pleopods may be 



