166 WILLIAM J. DAKIN 
surface of the lens was in contact with the face of the retina. 
A delicate non-nucleated sheath appears to bound the lens, 
but it is in all probability only the outermost layer of the lens 
substance. 
THe STRUCTURE OF THE RETINA. 
Very little trouble will suffice to show quite clearly the 
structure of the dioptrical part of the eye described above. 
The elucidation of the structure of the retina is a much more 
difficult task, and it is quite natural that this essential part 
of the eye has remained misunderstood. 
As we have already seen, the pigment band does not enclose 
the retina, but is made up of pigment granules lying within the 
retinal elements. We shall keep the term Rods for the real 
constituents of the rod layer, the part marked Re. in Balfour’s 
figure. This rod layer in poor, or even in moderately 
good sections, appears to be made up of rather long * rods’ 
separated by clear spaces. The ‘rods’ also have a peculiar 
broken-up appearance even when not cut obliquely, as appears 
most frequently to have been the case. Now as a matter of 
fact these dark-staining bodies are not the rods. Macera- 
tion preparations, but still more certain, transverse sections 
in the plane of the retina, show quite clearly that the rod layer 
is not exactly what it seems. It comes as a surprise, in fact, 
to discover that the dark-staming part of the rod layer 
appears in transverse sections as a grating or net (see fig. 8). 
It now requires the study of depigmented longitudinal sections 
and maceration preparations to explain the above. Really 
the explanation is simple. The retina is built up of one kind 
of unit only, and there are no supporting cells or other non- 
visual elements. Each visual unit consists of a rod-cell bearing 
a rod. 
The Rod-cells and Rods. Arod-cell (see fig. 2, and 
fig. 1, Rod-cell) consists of a columnar portion containing finely- 
granular protoplasm and crowded with pigment granules, and 
a proximal constricted and unpigmented part swollen out by 
the nucleus. As the rod-cells are numerous and the nuclei 
