PHOTOPHORES OF DECAPOD CRUSTACEA 379 



and progressively acquire the granular substance. Successive phases in this change 

 appear to be visible around the periphery of the organ. While the photophores on the 

 thoracic limb are supplied by a well-defined nerve, no trace of a nerve supply has 

 been found associated with the photogenic streak. On comparison with each other 

 these two organs show a curious inversion of parts (Figs. 14-16 and Plate XXV, fig. 3) 



(PP- 334-339)- . ^ J .... 



7. The photophores of S. affinis are described and compared with those of S. debths. 



Many of the photophores of S. affinis contain a prominent dense white substance, 

 possibly a xanthate or urate, which makes the organs conspicuous even in a long- 

 preserved specimen (Fig. 19 and Plate XXV, figs. 4, 5). 



While the pleopod photophores of S. affinis (Fig. 21) are very similar to those of 

 S. debilis, the uropod organs (Figs. 20, 22-4 and Plate XXVI, fig. i) contain highly 

 modified photogenic cells with no structure which can be readily interpreted as a 

 nucleus. The lenses of these organs are multiple and intracellular. 



Unlike the condition in Hoplophonis, the photogenic streak behind the last thoracic 

 limb (Fig. 25) contains photogenic cells resembling those of the pleopod organs, while 

 the organs on the limb itself (Figs. 26, 27 ; Plate XXV, figs. 4, 5 ; Plate XXVI, figs. 3-6) 

 bear a general resemblance to those in the same position in Hoplophonis, differing 

 however in their possession of the white substance already mentioned, which is deposited 

 here in the form of radially segmented spheres of a similar pattern to those seen in 

 Hoplophonis. The development of these spheres or "rosettes" appears to involve, as in 

 Hoplophonis, the degeneration of the nuclei of the cells concerned. 



The carapace organs (p. 360) resemble those on the thoracic limbs. 



Structures (Fig. 28) associated in life with red pigment spots on the telson and last 

 abdominal somite are described, and although not confirmed by their appearance in 

 section may prove to be luminous organs of yet another type (pp. 361-362). 



8. Information additional to that already existing is given on the photophores of 

 Systellaspis debilis. While in general the photophores are found in very similar positions 

 on the body and limbs to those in S. affinis, and while photophores of the two types 

 seen in 5'. affinis are present, there is no general concordance between these two species 

 with regard to the structure of the photophore in any particular position. For example, 

 the photogenic cells of the carapace organs of S. debilis (Fig. 30) resemble those of the 

 pleopod organs, while in S. affinis they are of the " rosette" type. Also the photogenic 

 cells of the organs on the fifth thoracic limb of S. debilis (Fig. 29) are of the pleopod type, 

 but in S. affinis(Fig. 26) these organs are closely packed groups of" rosettes " (pp. 363-368). 



The photophores on the telson in the two species correspond neither in position 

 nor in structure (Figs. 20, 28 and 31). 



9. In general the photophores of the Hoplophoridae can be distinguished as belonging 

 to one of two main types, that with elongated photogenic cells having a distal nucleus 

 and an area devoid of cytoplasm, and that formed of masses of radially segmented 

 non-nucleate structures. The distribution of these organs in those members of the 

 Hoplophoridae examined is shown in a table (p. 369). 



