368 



DISCOVERY REPORTS 



the distribution of crustacean photophores, these pigment spots, like those on the telson 

 of S. affi?tis, will be ventrally directed whenever the telson and uropods are brought 

 into play during the escape reaction of the animal, and will thus be visible from below 

 together with the other photophores of the body. 



The pigmented spots mark the position of clusters of radially segmented granular 

 deposits (Fig. 31) of the same pattern as those in some of the photophores of S. affinis 

 (p. 356 and Figs. 26, 27). They do not consist, however, of the same material as far as 

 can be judged, for by reflected light they are transparent and almost invisible. By 

 transmitted light they are seen in formalin-preserved material to be somewhat yellowish 



n.chit e, 



?■ 



phot. u. 



lOOU 



Fig. 31. The posterior telson photophore of Systellaspis debilis in surface view. The integument is trans- 

 parent and is not represented in the figure, n.chit.ep. nucleus of chitogenous epithelium ;/)/zo?.m. photogenic 

 unit ("rosette"). 



when unstained. Even when stained with carmine, which they take up readily, they 

 still possess a yellowish hue. The rosette-like spheres are grouped in a horizontal sheet, 

 ten to twelve spheres forming the posterior and about twenty spheres the anterior 

 photophore. Underlying them are apparent phases in their differentiation as in 

 S. affinis (p. 358, Fig. 27), and the whole organ is closely surrounded by a mass of closely 

 packed small dense nuclei resembling those of the chitogenous epithelium. 



No lens is present over the surface of these organs, and I have not been able to dis- 

 cover any trace of innervation. 



It will be realized that the telson photophores of S. debilis possess the structure 

 which might have been expected to be shown by the carapace organs. Their similarity 

 to some of the photophores of S. affinis renders the relations between the two species 

 still more obscure. 



The variety of photophores encountered in various situations on the body and limbs 

 in the members of the family Hoplophoridae which have been examined in the course 



