342 DISCOVERY REPORTS 



nerve fibres of the photophore nerve supply (Fig. 17 and Plate XXV, fig. 2, phot.c.nv.). 

 The granular zone of the pleopod organs and the basal caps of the carapace organ 

 may therefore be homologous. The photogenic cells of the pleopod and carapace 

 organs are, then, very closely similar in structure. 



It is noteworthy that not all the nerve fibres terminate on the basal cap of the photo- 

 genic cells ; on the contrary, only the central fibres of the bundle do so, while the peri- 

 pheral ones extend for some little distance down the walls of the photogenic cells. This 

 is clearly seen in the illustrations (Figs. 17, 18 and Plate XXV, fig. 2). The arrangement 

 of the nerve supply will be further discussed in describing the superficial view of the 

 photophores. 



Immediately ventral to the photogenic cells the chitogenous epithelium is profoundly 

 modified. Whereas its normal nuclei are flattened and densely staining, and are closely 

 applied to the inner surface of the chitin, here they are larger, ovate, and removed from 

 the chitin (Figs. 17, 18 and Plate XXV, fig. 2, n.r.c). They show less chromatin than the 

 normal nuclei, being almost uniformly lightly granular. Extending from the distal 

 ends of these nuclei to the inner surface of the chitin constituting the lens are bundles 

 of fibres (Fig. 17, r.c.b.) corresponding in number with the nuclei. The fibrous bundles 

 taper progressively as they approach the chitin, and their distal tips spread on to its 

 inner surface in a manner reminiscent of muscle attachment. These bundles may 

 possibly represent the cell bodies of the nuclei with which they are contiguous, and I 

 have provisionally identified them in this manner. 



Between the fibrous bundles are numerous spaces, having the appearance of vacuoles 

 (Fig. 17, vac.) entirely devoid of contents. For reasons given later (p. 344) I believe 

 that, although they do not contain coagulated blood, they may be fine blood channels 

 observed in transverse section. 



The tissue just described progressively merges with the general chitogenous epithe- 

 lium ventral to the lens. The nuclei become smaller and denser and the fibrous bundles 

 shorter and more diffuse in passing ventrally, until the normal appearance of the 

 chitogenous epithelium is regained at about the level of the ventral margin of the lens. 

 The function of this mass of tissue underlying the lens is uncertain. I am inclined to 

 believe that it is a reflector, and have accordingly named the ovate nuclei as being those 

 of the reflector cells. The possibility remains, however, that the fine fibrous bundles 

 are composed of secretion fibrils lying within the general cytoplasm of a syncytium, or 

 that the vacuole-like spaces are truly vacuoles and are indicative of secretory activity. In 

 this event the function of this zone may be complementary to the activity of the photo- 

 genic cells in the mechanism of light production, each producing an essential secretion. 

 Further investigation is clearly required before these questions can be answered. 



The integument lining the branchial chamber and forming the inner wall of the 

 branchiostegite is exceedingly delicate, and has beneath it a chitogenous epithelium 

 of the form already described. Enclosed between the inner and outer faces of the 

 branchiostegite is a haemocoelic space (Fig. 17, haem.) traversed by occasional strands 

 of connective tissue. 



