STUDIES IN THli RETINA. 343 



the I'adiating fibrils attaching them to the rest of the intra- 

 nuclear reticuhim can bo seen, perhaps because coated with 

 staining matter, but outside the nuclei these fibrils are appa- 

 rently too faint to be visible; at least, I have never seen them 

 except when they have occurred in the rods, in which cases, 

 again, their connecting threads are coated, with staining matter 

 (Part n, figs. 29 c, d, f ; while fig. 15 a of the same part 

 shows one flattened out against the membrane dividing the 

 inner from the outer limb of the rod, and two streams of 

 staining matter flowing from it, presumably along the 

 filaments with which it was associated). Fig. 29 c (Part II) 

 actually shows one of them upon a stained fiUiraent, along 

 which we may assume that it travelled. 



The origin of these " centrosomes" from nuclei seems to 

 be fairly widely acknowledged, and also their connection 

 with filaments. They occur in special numbers in ciliated 

 epithelium, apparently only as another form of the chromatic 

 basal bodies, to which we shall refer elsewhere. 



There is evidence, then, that these refractive deeply stain- 

 ing globules are merely parts of the stream of chromatin 

 passing outward through the retina. What else they may 

 be we cannot yet say. The difference between them and 

 other equally large, but less refractive and irregularly 

 shaped beads without clear vacuoles, may be due to slight 

 variations of physiological or chemical condition. 



While speaking of largo masses of chromatin leaving the 

 nuclei as masses, I may call attention to a curious phenomenon 

 found in the retina of the mouse and in some other vertebrates. 

 In all my preparations of mice, one or more very large clumps 

 are seen adhering to tlie walls of the nuclei — indeed, not 

 infrequently pi'otruding and standing out on the outer surface 

 of the nuclear membrane as sharply projecting knobs. I 

 have, however, never found any of them away from the walls 

 on any of the connecting filaments. I first noticed them before 

 I had discovered the general movement of chromatin from 

 nucleus to nucleus, and was naturally greatly struck by this 

 extra-nuclear chromatin, as was also my friend the late Mr. 



