30 n. M. BERNARD. 



seldom more than one deep. It is true that nuclei from this 

 layer do pass through the thick inner reticular layer to the 

 middle nuclear layer. Most sections will show, as has been 

 often noted before and variously interpreted, one or two 

 actually within the inner reticular layer. Further, all sections 

 sliow a number of nuclei in the innermost rows of the middle 

 nuclear layer so like the ''ganglionic cells" that they have 

 been recently freely claimed as being ''ganglionic," i. e. 

 as of much the same functional activity as the nuclei of the 

 innermost layer, which has always been the "ganglionic 

 cell " layer of authors. Although this resemblance need not 

 necessarily have anything to do with the question of migra- 

 tion, there cannot, to my mind, be any doubt but that the 

 "ganglionic cell" layer is drawn upon by the middle nuclear 

 layer, and may, indeed, for considerable tracts, be quite ex- 

 hausted (compare fig. 22, g.l. in a, h, and c). But such 

 a supply, at its best, would be insufficient to counterbalance 

 the drain on the middle nuclear layer. Further, as in the 

 case of the layer of rod nuclei, no mitotic divisions are found 

 in the " ganglionic cell " layer after the eye has once become 

 functional.^ 



We have therefore to seek elsewhere for the supply of 

 nuclei required by the middle layer to enable it to send so 

 many outwards through the outer reticular layer to become 

 the nuclei of the new rods. One would think the most 

 probable source for these nuclei would be the division of 

 those already composing the layer, but here again we are 

 baffled, for divisions do not occur, at least near or in the 

 places where they are wanted. Indeed, the primary object I 

 had in view in examining retinas killed at all hours of the night 

 was to ascertain whether it was not possible that, as no 

 divisions were ever seen in this layer in retinas killed during 



' I have seen a few traces of fragmentation which deserve attention, but 

 iiardly wide-spread enongh to meet the present difficulty. See also Borysie- 

 kiewitz's figures (' Unlersuchungen iiber den feineren Bau der Netziiaut,' 

 p. 19, 1887), which represent " twin ganglion cells." They certainly suggest 

 divisions of these cells, but are capable of a different interpretation. 



