66 H. M. BERNARD. 



streams in these fish retinas become more and more zigzag as 

 the meshes of the inner reticular layer get larger and coarser, in 

 the frog and toad, for some reason or other, the early straight 

 paths appear to become fixed. Whether this can in any way 

 be correlated with the other peculiarity pointed out in these 

 amphibian retinas, viz. that the absorbed matter passes by, 

 apparently without entering, the inner limbs of the rods, which 

 consequently remain very small, we are not yet in a position 

 to decide. It is, of course, quite possible that the physical 

 condition of the absorbed matter not coming in contact with 

 the staining matter in the inner limbs might be different, and 

 consequently its action on the cytoplasmic framework of a 

 retina might also be different. 



It need hardly be pointed out that if a group of such 

 streams as those shown in fig. 31, a,h, flowing through the laj^er 

 of rod nuclei were to combine in or just after leaving the outer 

 reticular layer (o.r.), and then flow on as one thick stream 

 through the middle nuclear and the inner reticular layers, we 

 should have the most developed type of "Miiller's fibre," such 

 as that shown in fig. 32, a. It is these most developed streams, 

 looking as if they were permanent structural elements in the eye, 

 which have alone been regarded as typical " M tiller's fibres." 

 Had all the minor forms of the same streams received equal 

 notice, the error could never have been made of ascribing to 

 them any fixed morphological significance. Such a wider 

 survey would also have saved Borysiekiewitz, to whose works 

 on the retina I should like here to express my indebtedness, 

 from his conclusion that the " Miiller's fibres " are tubes 

 conveying the nerve-fibrils to the rod layer.^ Ouly these most 

 developed strands which seem to rise directly from the rods 

 could possibly supply the necessary conditions, and, if this 

 conclusion were correct, we ought to find such developed 

 strands in all and throughout all the retinas of the whole of 

 the Vertebrata. This, as we have seen, is very far from 

 being the case. Equally mistaken, too, are the conclusions 

 based upon the impregnation method. In Ramon y Cajal's 



' ' Weitere Untcrsucliungcn,' Leipzig uiid Wien, 1894. 



