378 DISCOVERY REPORTS 



to be able to undertake some of these investigations on material available at Bermuda 

 and Woods Hole w^ith the aid of a Fellowship which has been awarded for the purpose 

 by the Leverhulme Trustees. 



VII. SUMMARY 



1 . The superficial photophores of Sergestes regalis are of an entirely new type. They 

 consist of horizontal sheets of interwoven fibres, in which the perpendicular photogenic 

 units, of doubtful origin, are scattered. There is no lens, and no associated nerve 

 supply has been discovered (pp. 310-314, Fig. i, and Plate XXIV, fig. i). 



2. Organs of Pesta (luminous liver tubules) are described in detail in Sergestes 

 corniculum, S. sargassi, S. diapontius, and S. edivardsi. They consist of compact groups 

 of modified liver tubules numbering as many as ten in S. cornicidum, visible from the 

 exterior through the integument, and showing well-marked zones of cytological 

 differentiation. Some of the cells composing the tubules show evidences of disruption 

 and shedding of their contents into the lumen of the tubule, while others are highly 

 vacuolated. Possible lens and reflector cells are also present. The pigmentation of 

 these organs in life is discussed, and their taxonomic significance mentioned (pp. 3 14-320, 

 Figs. 2-4, and Plate XXIV, figs. 2, 4). 



3. All the above-mentioned species of Sergestes also possess a linear photophore in 

 the roof of the branchial chamber. This organ is simple, without a lens or any well- 

 marked accessory structures, and is totally different from the organs in the same 

 position in S. challengeri (pp. 320-322 and Fig. 5). 



4. Photophores of endodermal origin in Parapandalus richardi are described. They, 

 like the organs of Pesta in Sergestes, are groups of modified liver tubules, but they are 

 of totally different structure from the organs of Pesta. It appears that similar organs 

 are not uncommon in the Pandalidae (pp. 322-327, Figs. 6-8, and Plate XXIV, figs. 3, 5). 



5. A simple structure on the pleopods of Parapandalus richardi, marked by a deep 

 red pigment spot in the living animal, has been examined, but whether or not it is a 

 photophore remains undecided. It consists merely of a diffuse mass of connective 

 tissue beneath the chitogenous epithelium, which is thicker here than elsewhere, but 

 does not appear to enter into the composition of the organ (p. 327 and Fig. 9). 



6. The species of Hoplophonis which have been examined show photophores differing 

 profoundly from those of Sergestes. The organs on the pleopods (pp. 329-334, Figs. 10- 

 12 and Plate XXV, fig. i) are closely similar to those of Systellaspis debilis (Kemp, 

 19106) and of S. affinis (p. 346 and Fig. 21). They possess a well-developed musculature 

 capable of orientating the whole organ with respect to the limb (Fig. 12). 



The photogenic cells of the carapace organs (pp. 339-344, Figs. 17, 18 and Plate XXV, 

 fig. 2) resemble those of the pleopod organs. 



The photogenic streak behind the base of the last thoracic limb, and the photophores 

 on the limb itself, are of an entirely novel type, and consist of clusters of radially seg- 

 mented granular masses, which are probably derived from cells which lose their nuclei 



