PHOTOPHORES OF DECAPOD CRUSTACEA 321 



remainder of its length, another 560//,, it slopes obliquely inwards on the roof of the 

 branchial chamber, so that its posterior end lies immediately above the most anterior 

 gill. 



Fig. 5. Transverse section through the photophore in the roof of the branchial chamber of Sergestes corniculum, a little 

 behind the level of the section shown in Fig. 2. Fixed Duboscq, Mallory's triple stain, chit. I. chitinous lens; c.t. connective 

 tissue; n.chit.ep. nucleus of chitogenous epithelium; n.phot.c. nucleus of photogenic ccW; phot. c. photogenic cell. 



The structure of the streak is indicated in Fig. 5. It is composed of extremely 

 narrow columnar cells (Fig. 5, phot.c), their limits only partially defined, converging 

 on a slight thickening of the integument (Fig. 5, chit.l.) forming the roof of the branchial 

 chamber. In conformity with this arrangement the cells are tapered, the elongated 

 nuclei (Fig. 5, n.phot.c.) occupying the inner broader ends, which show a denser 

 cytoplasm than the narrower ends. The nuclei, which are in general about half the 

 length of the cells, possess regularly scattered chromatin producing a granular appear- 

 ance. Some 30-40 cells make up the breadth of the organ. On its inner and outer sides 

 the cells of the organ progressively merge with those of the general chitogenous epithe- 

 lium (Fig. 5, n.chit.ep.), of which they are specialized portions. 



The thickening of the integument already mentioned is lens-like in section. It shows 

 two clearly defined layers of equal thickness, the outer of which is closely striated, and 

 the inner only slightly so. These layers are not distinguishable in the much thinner 

 chitin lining the branchial chamber, although this may be merely on account of its 

 delicacy. 



