344 DISCOVERY REPORTS 



In borax-carmine-stained whole preparations details of the photogenic cells are dis- 

 cernible, and Fig. i8 represents such a preparation in surface view. The general surface 

 of the integument is omitted from the figure, but the local thickening forming the lens 

 is indicated by vertical hatching to represent the striated appearance seen in this view. 

 Underlying the chitin are seen the nuclei of the chitogenous epithelium (Fig. i8, 

 n.chit.ep.), among which, but difficult to distinguish from them, are the nuclei of con- 

 tracted chromatophores. Above the lens the longitudinal row of photogenic cells is 

 clearly seen. Their nuclei are still more flattened and denser than those seen in 

 H. novae-zealandiae and H. grimaldii, but the cells again possess basal caps and associated 

 nerve fibres. Behind and below the photogenic cells lie the nuclei of the reflector tissue 

 (Fig. i8, n.r.c). 



It has not been found possible to trace out the further course of the nerve supply to 

 the photogenic cells. As seen in Fig. i8 the nerve bundles extend dorsally and lie 

 parallel with each other in the branchiostegite. Presumably they are all branches from 

 a single nerve, but this has not been observed, either in whole preparations or in 

 sections. Furthermore, it is not clear whether or not all the carapace organs are inner- 

 vated by branches from a single main nerve trunk. Further investigation, employing 

 suitable methods on properly fixed material, is necessary to elucidate fully the inner- 

 vation of these and other photophores. 



A constant feature of the carapace organs of the three species studied is their close 

 association with a prominent blood channel which runs horizontally in the branchio- 

 stegite from the posterior to the anterior end. On reaching each photophore, this 

 breaks up into a number of smaller channels, which, as far as can be seen in the whole 

 mounts of portions of the carapace, form a plexus in the tissues of the organ. It is 

 possible that these fine vessels, appearing in section, may give rise to the vacuolar 

 appearance noted between the fibrous bundles of the reflector tissue (p. 342 and Fig. 17, 

 vac). The fine vessels of the plexus reunite at the anterior end of the photophore to 

 pass on as a single channel to the next most anterior organ, where the same arrangement 

 is observed. The horizontal channel terminates at the most anterior photophore. This 

 distribution of the photophore blood supply has been most clearly seen in H. typiis 

 (Fig. 18, b.v.), but is apparent also in H. novae-zealmidiae and H. grimaldii, and is a 

 further illustration of the copious vascularization of photogenic tissues noted during the 

 course of this work. 



The absence of a definite chitogenous epithelium between the photophores and the 

 integument seems to indicate that they are of ectodermal origin. 



2. THE PHOTOPHORES OF SYSTELLASPIS AFFINIS (FAXON) 

 AND 5. DEBILIS (A. MILNE-EDWARDS) 



The existence of photophores in a member of the genus Systellaspis appears to have 

 been first noted by Perrier in 1886 in S.pellucida (Kemp, 19106, p. 643, as Acanthephyra 

 pellucida). Perrier's account, however, is of somewhat uncertain reliability, and the 

 first dependable account of the presence of photophores in a member of this genus was 



