434 TRANSACTIONS LIVERPOOL BIOLOGICAL - SOCIETY. 
made up of the Distal Cell layer (fig. 29, D.c.d.) and 
Outer Interstitial Cells (fig. 30, Zn.c.0.). This is Patten’s 
outer ganglionic layer and the Ganglienzellenschicht of 
Rawitz (36). 
(b) The layer of Rod Cells (Retinophorae—Stabchen- 
zellen (fig. 29, #.C.). 
(c) The layer of Rods (Stabchen) (fig. 29, Z.). 
The cells of the inner ganglionic layer of Patten, 
corresponding to the Zwischenzellen of Hesse, and what I 
shall call the inner interstitial cells, are to be found 
between the rod cells (fig. 30, Z. ¢.7.). 
Rod Cells.—-With regard to the minute histology of 
these structures much confusion exists. They form the 
most conspicuous portion of the retina in transverse 
sections, and are prominent as a layer of columnar cells, 
the basal proximal ends of which are continued as the 
rods forming another well-defined layer of the retina. 
The rod cell layer is thus the middle layer of the 
retina, lying between the layer of rods and the distal layer 
of cells, to be considered below. ‘The rod cells are of 
considerable length, and decrease gradually in thickness 
towards the periphery of the retina until, indistineuishable 
from nerves, they become connected with the fibres of the 
inner branch of the optic nerve (fig. 29, Op. n. 2.) which 
pass down outside the optic vesicle on all sides and unite 
to form the nerve branch under the eye. In order to 
study the details of a rod cell, sections must be cut in the 
plane of the retina and at right angles to the long axis of 
the eye-stalk. An examination of teased preparations is 
also necessary in addition to the sections. 
The rod cell increases gradually in diameter from a 
mere thread at the back of the retina to the typical 
columnar region. At about a fourth of its length is a 
slight varicosity, and a short distance further and nearer 
