PHOTOPHORES OF DECAPOD CRUSTACEA 



337 



(c) The transverse luminous streak behind the base of the fifth thoracic limb of 



Hoplophorus grimaldii 



The linear photophores behind the bases of the fifth pair of thoracic Umbs of Hoplo- 

 phorus are placed transversely and almost meet in the mid-ventral line. Laterally they 

 curve somewhat upwards and forwards, so that their outer ends are visible in surface 

 view on the posterior face of the limb base. In life these organs are deep violet-blue on 

 the surface, with a layer of shining orange-red pigment underlying the blue. After 

 preservation for some considerable time the organs were only visible as slightly raised 

 tracts of the integument with a more opaque appearance than the surroundmg area 

 owing to the density of the underlying tissue. 



These photophores have been examined in detail, and it is found that they show a 

 strong resemblance to the organ on the fifth thoracic limb of H. novae- zealandiae which 

 has just been described. The same phases of differentiation of the photogenic cells are 

 apparent, but they show a complete inversion of position compared with the similar 

 cells in H. novae-zealandiae. Whereas in the thoracic limb of the latter the recognizable 

 photogenic nuclei and early phases of their differentiation are on the side of the organ 

 remote from the integument, here they are superficial and adjacent to it. The inversion 

 of the photogenic tissue is very surprising, and cannot be readily explained. A study 

 of the photophores of Systellaspis affinis and S. debilis has, however, revealed com- 

 parable examples of the reversal of photogenic cells. 



The linear photophore of Hoplophorus grimaldii is illustrated in transverse section 



photc.4 



photc.3. 



photc.2. 



Fig 15 Transverse section through the luminous streak behind the base of the fifth thoracic hmb of Hoplophorus 

 orimaldit The haemocoele is indicated by mechanical stippling. Mallory's triple stain, chit, chitin ; cut. cuticle ; n.chit.ep. 

 nucleus of chitogenous epithelium; n.ref.c. nucleus of reflecting ctW; phot.c. i, pliot.c. 2, pitot.c. 2, phot. c. 4, phot.c. 5, 

 successive phases in the appearance of the photogenic cells. 



