STUDIES IN THE RETINA. 325 



distal fringe of the filaments of the pro torn itomic system^ 

 streaming from the rod-nuclei on to and into the rods; and, on 

 tlie other, we have quite irregular streaks of matter finding its 

 way out of the rods and along the syncytial framework as 

 described and figured in Part V. 



The connection between the strias of the rod and the 

 reticulum of the rod-nucleus is shown in figs. 18 d and 21, 

 selected from many others. A rod-nucleus is shown in the 

 former figure connected by filaments proximally with the 

 nucleus behind it, while, distally, its own filaments are 

 collected into a bundle which is limited by the outline of the 

 rod. The same might also have been gathered from what 

 has been described of rod-formation in Parts I, II, and IV. 

 We saw there that each rod was a protrusion from the retinal 

 syncytium of a vesicle which forced back the pigment cells — 

 each vesicle being apparently dominated by a single nucleus. 

 Threads descended from the nucleus on to and into the rod- 

 vesicle with clumps of staining matter upon them, and were 

 hence often referred to as staining threads.^ Although, in 

 these earlier papers, no special stress was laid upon the fact 

 that these threads came from the nucleus, it was quite clearly 

 stated, and figures were given to show that this was the case ; 

 for instance, Part II, fig. 29, and page 454, 



The fig. 21 a, from the human retina, was selected because 

 the peculiar and probably accidental arrangement of the 

 chromatin masses within one of the nuclei made the connec- 

 tion specially clear. Faint suggestions of symmetry in the 

 arrangement of the chromatin masses had frequently attracted 

 my attention; I find in my notes figures of rod-nuclei with 

 the chromatin arranged in approximate meridians ; others in 



' The expression "staining tiiread" was meant, to describe the appearance 

 shown in these figures. But we now know that this description is not really 

 correct. It is true that tlie tlireads which form the longitudinal strise down 

 the rods are best seen when rendered visible by being coated with deeply 

 stained matter, but at times, e. g. wiien inner and outer limbs of tlie rods 

 have been partly pulled asunder, or when the staining matter is collected 

 into disconnected clots, short stretches of the threads tiiemsclves become 

 visible, but, being quite hyaline, are estreinely difficult to see. 



