352 



DISCOVERY REPORTS 



this granular mass appears to correspond closely with that seen at the base of the 

 photogenic cells of the pleopod photophores of Hoplophorus and Systellaspis ajfuiis 

 itself, and even more closely with the non-staining granular zone of S. debilis (Kemp, 

 19106, p. 644). For the reasons which follow, however, I do not believe that this is so. 

 Close examination of the uropod organs of S. affinis shows the presence of minute 

 lenticular bodies resting in the distal concavities of the granular masses (Fig. 23 , phot.c.b.c). 

 They stain readily with acid fuchsin, and present a finely punctate appearance, strongly 

 recalling the basal cap of the carapacephotophores of //o/)/o/)Aon«(Fig. 17,^/^0^. f. 6. c), with 

 which I believe them to be homologous. Earlier (p. 342), I gave reasons for my belief 



that the basal cap of Hoplophorus is homologous with 

 the granular zone of the pleopod organs of Hoplophorus 

 and Systellaspis. It would therefore appear that the 

 basal cap, and not the granular mass of the uropod 

 photogenic units, corresponds with the granular zone 

 of the pleopod photophores mentioned. 



The proximal granular mass, then, is a structure 

 of an entirely new type and is additional to those 

 already seen in the pleopod organs. It forms a com- 

 pact reflector behind the photogenic units, where its 

 '.U.d, efliciency is no doubt enhanced by the possession by 

 each block of granules of a distal concave surface. 



The pattern of arrangement of the photogenic units 

 within the organ leaves little doubt of their homology 

 with the photogenic cells of the pleopod photophores, 

 although the relation between the nucleus of the 

 pleopod photogenic cell and the distal structures of 

 the uropod photogenic unit is far from clear. It is 

 difficult to see in these distal structures any repre- 

 sentative of a nucleus, and in the absence of further 

 information I do not intend to speculate on the fate 

 of the nucleus which the photogenic cell undoubtedly 

 once possessed. Only an investigation into the 



photu. 



:c.b.c. 



pr.gr. m. 



Fig. 23. Diagram of a single photo- 

 genic unit of the uropod photophore 

 of Systellaspis affinis. phot.c.b.c. basal 

 cap of photogenic cell; gr.t. granular development of the photophores, for which a supply 



tip; l.s. lens-like septum; phot.ii.cl.a. of material would be difficult to obtain, can elucidate 



the problem. The position of the lens, within the 

 distal tip of the "cell", is to some extent paralleled 

 by the condition seen in the eye of the serpulid worm 

 Branchiomma (Dahlgren and Kepner, 1908, p. 241). 

 Here the elongated hypodermal cells secrete a lens 



in their distal cytoplasm, but a lens-shaped nucleus is retained. It will be shown later 



(P- 358) that some cells of other photophores of Systellaspis affinis, like those of 



Hoplophorus, also lose their nuclei. 



clear area of photogenic cell ("unit"); 

 pr.gr. m. proximal granular mass ; st.z. i , 

 first structureless zone; st.z. 2, second 

 structureless zone; str.l. striated layer; 

 vac.z. vacuolated zone. 



