48 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



cells, which alternate with these, are pigmented likewise, but the pigment 

 is not so abundant and lies in the periphery of the cell body, leaving free 

 a highly refracting central axis. 



If the relation of these cells to each other has been made sufficiently 

 clear, it will be understood that, in accordance with Schewiakoff s scheme 

 of the structure, sections that cut the retinal cells transversely give very 

 different appearances at different levels. A section through the very 

 tops of the retinal cells, that is, the last section of the retina before 

 striking the vitreous body, would show large polygonal areas of heavy 

 pigment (the ends of the pigment cells), in between which would lie the 

 much smaller, less pigmented, highly refracting ends of the visual cells 

 ('89, Taf. II, Fig. 19). A section lower down in the retina, that is, more 

 toward the centre of the club, would strike the low-lying enlarged central 

 portion of the visual cells with their contained nuclei, and the smaller, 

 proximal ends of the pigment cells. It would, therefore, give the reverse 

 appearance from the preceding section, namely, that of large unpig- 

 mented (or but slightly pigmented) areas (the swollen bodies and nuclei 

 of the spindle-shaped cells), and in between them smaller pigmented 

 areas, the ends of the proximally tapering pigment cells ('89, Taf. II, Fig. 

 20). A section on the other side of the one first described, that is, one of 

 the first through the vitreous body, would show pigment areas of the 

 same size as the large ends of the pigment cells (the cone-shaped streaks 

 of pigment in the vitreous body which according to Schewiakoff are 

 associated with the pigment cell), and in between them the cross-sections 

 of the rod-like processes from the visual cells, lying in canals in the clear 

 homogeneous ground-substance of the vitreous body ('89, Taf. II, Fig. 18). 



Let me give a resume of Schewiakoff's conception of the structure 

 of the retina. 



a. There is an alternation of pigment and visual cells, the nuclei of 

 the spindle-shaped visual cells lying at a lower level than those of the 

 cone-shaped pigment cells. 



b. From the visual cells extend rod-like processes into the vitreous 

 body, lying in canals in the latter. 



c. In the vitreous body a cone-shaped streak of pigment overlies 

 each pigment cell of the retina, which is not a part of that cell. 



d. Apart from these pigment streaks and the rod-like processes of 

 the visual cells the vitreous body is structureless, probably a secretion of 

 the pigment cells. 



My own work, now, has led me to a different conception, so that my 

 conclusions on the same points would be as follows : 



