320 DISCOVERY REPORTS 



tubules up to the termination of the highly vacuolated zone. The upper erupting and 

 rod-containing zones of the tubules appear to form the upper white portion of the 

 organ in Burkenroad's description (1937). In preserved and sectioned material the 

 limits of the carmine pigment cap cannot be determined. 



The optical and physiological qualities of Pesta's organ, if it be truly a luminous 

 organ, can only be suggested. It is possible that the dorsal cells with their contained 

 refractile rods, together with the dorsal external pigment cap, form a reflector; that the 

 ventral lenticular termination of the tubule acts as a lens; and that the intervening 

 zones of cells are concerned in the active production of light. Whether the vacuolated 

 or the erupting zone, or both, form the centre of luminescence, or whether the lumen 

 of the tubule itself may be occupied by a luminous secretion, is of course a matter for 

 speculation, but the tentative suggestion may be oflrered that it is the lumen of the 

 tubule itself which contains the luminous material. 



It was first shown by Dubois and later abundantly confirmed by other workers that 

 the production of luminescence in arthropods results from the interaction of the sub- 

 stances luciferin and luciferase in the presence of oxygen and water. (A convenient 

 review, with a valuable reference list, of work on the physiology of light production 

 in the arthropods is given by Maloeuf (1937).) It is possible that the vacuolated and the 

 erupting zones of cells in the tubules are concerned with the production and discharge 

 into the lumen of the tubules of these two substances, luciferin and luciferase. Certainly 

 the appearance of the cells suggests the active production of two dissimilar substances. 

 If this is correct the lumina of the tubules are the seat of light production. Harvey 

 (1919), however, states that in the ostracod Cypridina hilgendorfii the enzyme luciferase 

 alone is located in the photogenic cells, the luciferin being distributed in various 

 tissues. Whether this is so in Crustacea generally is unknown. But until the organs of 

 Pesta have been unequivocally shown to be photophores and their physiology to some 

 extent elucidated further speculation is unwarranted. 



3. THE BRANCHIAL CHAMBER PHOTOPHORES OF SERGESTES CORNI- 

 CULUM, S. SARGASSI, S. DIAPONTIUS, AND S. EDWARDSI 



While examining the liver photophores of the above species, a glandular streak 

 extending longitudinally in the roof of the branchial chamber was observed in all the 

 specimens. There is considerable reason for regarding this structure, provisionally at 

 least, as a photophore. It occupies precisely the same position as the organs noted by 

 Hansen (1903) on the lateral face of the branchiostegite of S. challeugeri, and later 

 shown by Kemp (19106) to be internal, facing inwards and downwards on to the gills. 



The glandular streak is rather less than i mm. in length in a specimen of S. corni- 

 cidiim measuring 4-2 cm. It is first seen in a section a little behind the level of the 

 section illustrated in Fig. 2, where it lies on the inner face of the lateral wall of the 

 branchial chamber just below its junction with the body. It runs backwards at this 

 level for some 80 ^i, and then, without interruption, turns on to the roof of the branchial 

 chamber, and extends backwards parallel with the body for a further 240 /i. For the 



