70 H. AI. BERNARD. 



absorbed in large quantities^ all the elements are permanently 

 of this character, but away from the centre only oue here 

 and there has its inner limb enlarged. Borysiekiewitz refers 

 this to the protrusion of the nucleus, but as the nucleus is 

 not always protruded, I prefer to refer it to an extrusion of 

 fluid from the retina. Not only does the early protrusion of 

 fluid vesicles from the retina in the first stages of rod- 

 formation make this probable, but also the fact that globules 

 of fluid are continually escaping from the retina into the 

 rods, as described and figured in Part II. 



The striation of the rods, which has long been known, has 

 now been traced to its true cause, viz. the existence of 

 strands, sometimes taking stain, in the walls of the rod 

 vesicles, while the lumina of these vesicles are occupied by a 

 staining network in connection with these strands. 



The refractive matter which fills the outer limbs 

 of the rods is absorbed pigment, which is usually, 

 but not always, clarified during the process of 

 absorption* The correlation of this with the results of the 

 classical researches of Boll, Kuhne, Ewald, and others I am 

 not in a position to work out, for reasons given in Part V. It 

 must be left to time, on the one hand, to show where we 

 mutually confirm one another, and, on the other, to eliminate 

 our respective mistakes. Had I commented on all the results 

 obtained by previous workers whenever they overlapped the 

 subject in hand, these papers would have been lengthened 

 out indefinitely ; as it is, the histological details given in them 

 have had to be limited to a small selection of those available. 



The curious zone formation within the retinal syncytium 

 has been traced largely to the above-mentioned lateral move- 

 ment of the nuclei of the middle layer from the rim towards 

 the centre. 



The " Miiller's fibres/^ however startling they may appear at 

 their highest development, are merely streams of the pigment 

 matter which have been absorbed by the rods, and which, 

 witli many interesting variations of detail, pass inwards 

 through the retina, eventually to join the vitreous humour. 



