STUDIES IN THE RETINA. 347 



and, losing the long cylindrical shape, pass into the many- 

 layered spindle-shaped nuclei attached by radially arranged 

 cytoplasmic strands to the two limiting membranes of the 

 retina. Here, again, we may find fluid vesicles at the distal 

 ends of some of these cytoplasmic strands (figs. 23 a, h, c), 

 which, as we move in towards the centre of the retina, 

 protrude further and further beyond the external limiting 

 membrane, as the first beginnings of rods. Again, individual 

 nuclei well within the retina may even be here and there 

 seen with a vesicular excrescence, into which the nuclear 

 reticulum sends out radiating filaments (fig. 23 h). These 

 phenomena speak for themselves. They link on perfectly 

 naturally with the different stages of rod-formation already 

 described in former parts. I am especially tempted to call 

 attention to the analogy between these long cytoplasmic 

 strands with their terminal vesicles and the long thin cones 

 which swell into vesicles after passing through the rod-layer. 

 The point which at present claims our attention, however, 

 is the fact that the fluid which causes these vesicles and 

 eventually swells them into rods can, so far as microscopical 

 appearances go, only have come from their respective nuclei. 



We come once more to the question — whence do the rod- 

 nuclei receive their supply ? A comparison between the 

 sizes of the rods and the sizes of the nuclei shows that no 

 nucleus could protrude a rod from its own fluid contents. 

 In order to fill a rod it must pass on fluid which it receives 

 from elsewhere. And this brings us to a phenomenon which, 

 so far as I can explain it, points to a systematic pulsation of 

 the retinal nuclei, a pulsation which sends the fluid through 

 the retina outwards and into the rods. 



Let us take first the microscopic appearances which suggest 

 the existence of pulse waves through the retina. The first 

 is the fact that, in every well-preserved retina, in addition to 

 the nuclei which may be considered normal, are others in 

 great numbers in two opposite phases. On the one hand, 

 we have large vesicular nuclei with scattered chromatin, and, 

 on the other, either small round nuclei with compact chro- 



