50 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



occasionally be demonstrated, which areas are the pyramid cells. In 

 Fig. 2, the more definite polygonal outline as well as the lighter shade 

 of these areas was a distinguishing feature. The difference in shade 

 was not wholly due to a difference in pigmentation but to a 

 structural difference. 



The nuclei of these cells are usually a little larger than those of 

 the prism cells and are filled with a finer and less dense network 

 (Figs. 4 and 7, npyr), in consequence of which they present a lighter 

 appearance in sections when examined with a high power. It will be 

 seen in the figures (4, 7) with what regularity these lighter nuclei 

 lie opposite the pyramids. Some few exceptions occur. These are 

 probably due to the fact that a nucleus or pyramid was not differenti- 

 ated by the technique. If this opposition between the pyramids and 

 the lighter nuclei were all, I believe it would be sufficient evidence 

 for associating these lighter nuclei with the pyramid cells.* 



(c) The long pigment cells are about as numerous as the pyramid 

 cells. In these cells, as in the prism and pyramid cells, three regions 

 can be distinguished : the region of the nucleus, a pigmented region 

 (the distal half of which extends between elements of the vitreous 

 body), and a distal rod-like portion, or fiber, which is continued 

 between the prisms into the capsule of the lens (Figs. 4, 7, 9). The 

 pigmented portion is about twice the length of that described for the 

 other cells, and also often of greater diameter, so that in transverse 

 sections (Figs. 1, 2, 3) these cell-areas are larger than those of the 

 other cells. As nearly as I could determine, these cells are pigmented 

 just like the other retinal cells described. In quite unpigmented series, 

 however, they often contain more pigment than the other cells do 



* I go into this at some length because the cell-walls in the series that 

 showed the nuclei best differentiated as lighter and darker ones did not show 

 well, and there might be some doubt that these lighter nuclei belonged to the 

 pyramid cells. I could, however, in many instances, trace the axial fibers of 

 the pyramids through the pigmented zone to these lighter nuclei (as already 

 noted) which fact can leave no doubt but that some of these nuclei belong to 

 the pyramid cells. (Similar nuclei, however, are found to belong to the long 

 pigment cells, to be described below.) Centrad these pyramid cells are continued 

 into a single process just as the prism cells were shown to be (Fig. 7). Figures 

 6, 8, 9, and 21 show samples of all the pigmented cells found in macerated 

 preparations, and none of these (except Fig. 9, long pigment cells) show more 

 than a single centrad process. Hence, I conclude that centrad both the pyramid 

 cells and prism cells are continued as a single prolongation. 



