590 William Patten 



most highly inodifìed ganglionic ones. Those nerve fibres, which arise 

 directly from the ganglionic brandi, may be considered as the inner euds 

 of ganglionic cells, the nucleated bodies of which in the earlier stages 

 bave become entirely separated from the retina. The ganglionic layer 

 then contains cells in ali stages of ganglionic perfection, and showing ali 

 grades of union with themselves and with the real sense organs, — the 

 retinophorae and their rods. 



Having traced ali these fibres to the rods, it remains to see how 

 they terminate there. In cross or longitudinal sections, they are extra- 

 ordinarily difficult to see, but, by isolating the rods hardened in hot 

 chromic acid, the difficulties will be materially diminished. By the latter 

 method then, one may see the surface of the rods covered with longitu- 

 dinal fibres, from which arise innumerable, smaller branches encircling 

 the rods with a meshwork of fibrillae (PI. 29, fig. 20). The larger, 

 longitudinal fibres, instead of growing gradually smaller toward the 

 inner extreniity of the rod, retain their originai size, and, dividing into 

 one or two branches, unite with each other by arched loops (PI. 29, 

 fig. 22). From these external loops may arise a few minute fibrillae, 

 which extend over the inner end of the rod. AH these fibres adhere so 

 firmly to the surface, tbat it is extremely probable the ultimate fibres 

 penetrate the rod and become continuous with the cross fibrillae of the 

 axial nerve. The latter, as we bave already said, after issuing from 

 one side of the extremity of the rod, divides into two branches ; one of 

 which unites with the axial nerve of the neighboring celi, or, in some 

 cases, passes over the end of one rod to unite with the nerve of the next; 

 the other, bending completely double, passes between two adjacent 

 rods, over the surface of which its branches are distributed. 



A remarkable peculiarity will be observed by examining the inner 

 surface of a group of detached rods; it will there be seen that the 

 loops of the axial nerves are ali turned in the same di- 

 rection. It is not improbable that some relation exists between this 

 fact, and the originai arrangement of the two cells, by the fusion of 

 which the retinophorae were formed. In the very best preparations, the 

 most careful examination failed to discover any trace of a division in the 

 rods, similar to that found in those of Arca. 



On the periphery of the retina, the rods are absent, and the retino- 

 phorae reduced to slender fibres, the nuclei of which are difficult to 

 distingnish from those of the inner, ganglionic layer. In fact, at this 

 point, the retinophorae, and the inner ganglionic cells, together with 

 many nerve fibres from the outer ganglionic layer, form an inextricable 



