PLATE XXVI 



Fig. I. The left uropod photophore of Systellaspis affinis seen in tiiick 

 (loo^) transverse section. Compare with Fig. 24. Mallory's triple 

 stain. X no. l.s. lens-Hke septum across the photogenic unit; 

 phot.nv. nerve to photophore ; phot.u.cl.a. clear area of photogenic 

 unit ; phot.u.p. proximal granular mass of photogenic unit. 



Fig. 2. Right lateral view of the cephalothorax of Systellaspis affinis, 

 showing the photophores near the inferior margin of the branchio- 

 stegite, and the position, indicated in white, of the transverse streak 

 behind the base of the last thoracic limb, x 2 approx. phot.c.m. 

 photophores on the carapace margin ■,phot.t.s. photogenic transverse 

 streak. 



Fig. 3. Section passing through the periphery of the proximal photo- 

 phore on the propodus of the fifth thoracic limb of Systellaspis 

 affinis showing the photogenic nuclei before their degeneration. 

 Compare with Fig. 26. Mallory's triple stain, xiio. phot.n. i, 

 photogenic nucleus before degeneration; phot.n. 2, advanced stage 

 in the degeneration of a photogenic nucleus ; />Ao/.«. i, photogenic 

 units with first segmentally disposed deposits of the granular sub- 

 stance seen in Plate XXV, figs. 4, 5. 



Fig. 4. The photogenic streak (seen in Plate XXV, fig. 5) on the pro- 

 podus of the fifth thoracic limb of Systellaspis affinis. Mallory's 

 triple stain, x no. phot.u. i, phot.u. 2, stages in the differentiation 

 of the photogenic units (granular "rosettes"). 



Fig. 5. Section passing through the photophore at the proximal end of 

 the carpus of the fifth thoracic limb of Systellaspis affinis. Suc- 

 cessive stages in the differentiation of the granular "rosettes" are 

 clearly seen. Mallory's triple stain, x 240. phot.n. i, phot.n. 2, 

 stages in the degeneration of the photogenic nuclei; phot.u. i, 

 phot.u. 2, stages in the differentiation of the "rosettes". 



Fig. 6. Part of the longitudinal photogenic streak on the fifth thoracic 

 limb of Systellaspis affinis, enlarged from the section seen in 

 Plate XXVI, fig. 4. The radial segmentation of the granular spheres 

 visible in those indicated phot.u. 2. x 240. 



