PHOTOPHORES OF DECAPOD CRUSTACEA 



311 



on the exopod, while the external ramus of the uropod had "a row of four near the 

 middle and another row of two or three at the distal end, the foremost in line with the 

 tooth of the outer margin". 



At the time when I examined the appendages, however, no trace of colour remamed 

 in these organs, and it required close examination to determine their position. Although 

 colourless, the organs showed in surface view as small rather opaque areas possessing 

 a faintly mosaic or granular appearance. Both the maxilla and uropod were sectioned 



for examination. 



Study of the sections revealed the presence of well-defined structures (Fig. i a, b; 

 Plate XXIV, fig. i) occupying precisely the positions described by Dr Kemp, with the 

 exception that the exopod of the maxilla bears four, not three, of these organs. Three are 

 arranged almost in a longitudinal row, ahhough the second is somewhat lateral to the 

 first and third; while the fourth, which is larger than the other three, is placed on the 

 opposite (morphologically anterior) side of the exopod. This last organ is illustrated in 



the figures. 



The integument overlying the organ is not markedly differentiated from the adjacent 

 surface of the limb, so that there is no lens as in the superficial photophores of 

 S. challengeri (Hansen, 1903) and S. lucens (Terao, 1917 as 5. prehensilis). At most, both 

 cuticle and chitin may be somewhat thicker than elsewhere on the limb. The main mass of 

 the organ beneath the integument is composed of fibres arranged in successive parallel 

 sheets (Fig. i a, fib.), the fibres composing each sheet being interwoven in the horizontal. 



photcen 



\_ photcen supih. haem 



nuc.fibm.c. 



nucfib. 

 m.c 



Fie I a Part of a longitudinal vertical section through the maxillary exopod of Sergestes regalis, showing one of the photo- 

 Zrl A photograph of the section appears in Plate XXIV, fig. i. b. Part of one of the photophores seen ,n horizontal 

 sec° on at the leTef of the photogenic centres, to show the inter^voven fibrous tissue. Both fixed Duboscq Ma lory's tnple stam. 

 Srchill^^rinterwove'n fibnls ; haenu haemocoele of the l.mb ; rn..fib.nuc. nucleus of fibnl mother cell ; phot.cen. photogenic 

 centre; sup.fib. superficial fibres. 



