STUDIES IN THE RETINA. 463 



fractive matter. This, as we have seen, is absorbed by the walls 

 of the rods filling tliem up till they are turgid. This matter 

 would thus find its way inevitably up against the transverse 

 membrane separating inner from outer limb, and, seeing that 

 it passed through the outer wall into the rod, there is no 

 apparent reason why it should not pass through this transverse 

 membrane from the outer limb into the inner limb. This, 

 then, I believe, is what takes place, the very form of the 

 ellipsoid being suggestive of its having been forced through 

 to form a kind of drop on the proximal side of the transverse 

 membrane. Confirmatory evidence will later be adduced from 

 other retinas, but sufficient to establish the point will be 

 found in what follows. 



When we come to the ellipsoid in the cones (see figs. 

 15, c — e) it would seem that the explanation we have given 

 of it in the rod could hardly apply. There appears to be a 

 transverse membrane (fig. 29, /, j), but there is no swollen 

 outer limb filling up with refractive matter. Nevertheless 

 the explanation of the ellipsoid is practically the same, as 

 we can gather from the conditions seen in the frog. In the 

 cones of the frog there is invariably a round refractive globule 

 at the junction of the basal and the conical portion. In 

 Avell-staiued specimens a mass of staiuiug matter is generally 

 seen abutting against this globule, as if they uiutually blocked 

 the way for one another. We thus get practically the same 

 condition as in the rod, though in this case we do not know 

 exactly where the transverse membrane is, i. e. whether the 

 refractive globule is on its inner or outer side. 



This parallel assumes (1) that the refractive globule of the 

 cones of the frog is of the same substance and has the same 

 source as the refractive matter in the rod, and (2) that this 

 refractive globule and the adjacent staining matter will later 

 fuse together to form the definitive ellipsoid. 



The former of these assumptions is, I think, fully justi- 

 fiable. We have seen how readily pigment granules cling 

 to the thin protoplasmic walls of the cones, and can be seen 

 fading away on the fine membranous walls of the inner limbs 



