282 



Fig. 2. 



DARK. 



ûhte(fbr.r.) to the first optic ganglion [gn.opt.), where it terminates; 

 and finally a few accessory cells {cl.su.) containing a whitish pigment 



and extending from the proximal part 

 of the retina through the basement- 

 membrane toward, but not into, the 

 first optic ganglion. 



In eyes which had been sub- 

 jected to the light for somewhat over 

 two hours, the pigment in the ac- 

 cessory cells (Fig. 1 , cl.su.) showed 

 two regions of concentration, one in 

 the proximal part of the retina , the 

 ■A |Ê 1\ /i other near the distal surface of the first 



M\ /■ |\ /I opticganglion. These were about equally 



■ \ iM . iU l^ conspicuous and usually connected by 



numerous pigmented strands. In an 

 eye kept some two hours in the dark 

 (Fig. 2), the concentration near the optic 

 ganglion had largely disappeared, and 

 the great bulk of the pigment was lo- 

 cated in the proximal part of the retina. 

 The movement of this pigment from the 

 retina proximally to the position near 

 the first optic ganglion, as induced by 

 light, was accomplished in from forty- 

 five minutes to an hour , and the re- 

 verse movement, which took place in 

 the dark, was completed in from one 

 and three-quarters to two hours. 



In an eye exposed to light, the pig- 

 ment in the proximal retinular cells 

 (Fig. I, cl.px.) was distributed almost 

 uniformly through the retinal fibres 

 and the bodies of the cells; there were, 

 however, two slight concentrations, one 

 at the distal ends of the cells and an- 

 other around the rhabdome. In an eye 

 kept in the dark (Fig. 2) , the pigment 

 was located entirely in the retinal fibres 

 proximal to the basement membrane. The movement of the pig- 

 ment from its proximal position to its distal one under the influence 

 of light was accomplished in from thirty to forty- five minutes; the 



■^S-i^i--:.-gn.ofii. '?5;'&-'"---=' 



Fig. 1. Ommatidium from a 

 retina subjected to the action of 

 light for some-what more than two 

 hours. 



Fig. 2. Ommatidium from a 

 retina kept in the dark for about 

 the same length of time. 



Abbreviations : cl.dst. distal 

 retinular cell; cl.px. proximal re- 

 tinular cell ; cl.su. accessory cell ; 

 con. cone; cm. corneal hypoder- 

 mal cell; eta. corneal facet; fbr.r. 

 retinal nerve fibre; gn.opt. first 

 optic ganglion ; mb. ha. basement 

 membrane; rhb. rhabdome. 



