456 H. M. BERNARD. 



I'etina. The fluid vesicle in the ordinary course of things 

 would, on approaching the mem. lim. externa, form the usual 

 conical protrusion, and into it the staining reticulum would 

 follow. On the other hand, it is only fair to note that 

 streams of very delicate staining reticulum occur elsewhere ; 

 one other, for instance, is shown running up from the left- 

 hand rod-nucleus in fig. 27. The explanation of this must 

 be deferred until I can at the same time give the evidence 

 in full on which it rests, and this I hope to be able to do in 

 the near future. 



Further Contents of the Rod. — So far, then, we have 

 described the origin and structure of the rod as a protoplas- 

 mic pi'otrusion from the retina, containing the usual staining 

 network very strongly developed in the outer limb, and with 

 some clear fluid in the meshes or interstices. 



This network and this fluid are not, hoAvever, the sole 

 contents of the normal rod, and the striking difference 

 between inner and outer limbs, apart from the difference 

 in sli ipe and density of the reticulum, is found in the fact 

 that while the former remain protoplasmic vesicles, with 

 apparently soft, flexible walls filled with these elementary 

 constituents which we have described (passing over for the 

 moment the ellipsoid), the outer limbs become filled with 

 some highly refractive substance, which renders them turgid. 



The change from the loose, long terminal bag found at 

 the tip of the advanced cone (c^) to the outer limb of the 

 rod (r^) (see Part I, PL 3, fig. 4) is seen to consist not only 

 in the squeezing outwards of the staining matter to the 

 distal end of the inner limb, but also iu the filling up of 

 the outer limb. Now while we have traced to its source 

 some of the matter which helps to fill the outer limb, viz. 

 the staining reticulum, this will not account for the refractive 

 contents which now seem to make them turgid and cylindrical. 

 Further, we saw that the outer limbs of the rods lengthened 

 (from Ti to rg), and hence apparently continued to take in more 

 of this refractive constituent of their contents ; and not only 

 lengthened, but as a rule became also much thicker, I have 



