338 



DISCOVERY REPORTS 



in Fig. 15. The integument overlying it shows the usual differentiation into cuticle and 

 chitin (Fig. 15, cut. and chit.) and is not markedly developed to produce a lens-like 

 formation. It appears to carry in life a violet-blue pigment similar to that noted by 

 Kemp (19106, p. 644) in Systellaspis debilis, and which is found in the photophores of 

 Decapoda generally (1910Z), p. 640). Underlying it the chitogenous epithelium is very 

 thin for the most part and with only scattered nuclei. Here and there, however, 

 occur closely packed groups of larger nuclei, one of which (Fig. 15, ti.rhit.ep.) is 

 found in the proximity of the photophore, but has no functional connexion with it. Its 

 presence, however, may perhaps be taken as indicating that whatever the origin of the 

 photophore it is not derived from the ectoderm. 



As in the previously described photophore (Fig. 14) the main mass of the organ 

 consists of the photogenic cells in various stages of differentiation (Fig. 15, phot.c. i, 2, 

 3, 4, and 5) and nuclei which probably belong to the reflector layer (Fig. 15, n.ref.c). 

 The reflector layer in all likelihood carries a red pigment similar to that found in 

 HoplopJiorus novae-zealandiae (p. 336); this, together with the yellow colour which 

 may be supposed to be associated with the actual photogenic cells, would give rise to 

 the underlying shining orange-red pigment already mentioned (p. 337). 



Stages in the presumed growth and differentiation of photogenic cells are illustrated 

 in detail in Fig. 16. On the extreme right of the figure at a is illustrated a photogenic 

 nucleus (Fig. 16, n.) of the type found lying near the surface of the organ. It almost 

 completely occupies a space bounded by a membrane which may reasonably be inter- 

 preted as a cell membrane (Fig. 16, cm.), but no trace of cytoplasm has been found 

 enclosed by it. The nucleus shows a reticulate pattern in the distribution of its chromatin, 

 and in most instances a prominent nucleolus has been observed. At b is shown a later 

 stage wherein the nucleus {d.n.) gives every indication of degeneration, but still often 



25^. 



V.Z. 5,2.' 



VI 



si' ' dh. nl. b.c. cm. ' n. nl. 



Fig. 16. Part of the preceding section enlarged to show the details of the photogenic cells. The arrow points 

 to the external surface of the photophore. Blood channels are indicated by mechanical stippling, but the remainder 

 of the haemocoele is left white, b.c. blood channel; c.b. central body; cm. cell membrane; d.n. degenerating 

 nucleus; n. nucleus; nl. nucleolus; s.s.^ early stage in the production of the radially segmented zone; s.z.^ later 

 stage of the segmented zone; v.z. vacuolated zone. 



