614 HOWARD. [Vor. XIX. 
that of another. Such an effect may be produced in a 
cylinder of glass which under ordinary conditions is isotropic; 
pressure at each end will produce polarization in the negative 
optical direction with respect to the cylinder axis, while ten- 
sion at the same points will produce a positive reaction to 
the light. The latter would represent the normal condition 
in the outer segment of the rod; 7. ¢., the axis of maximum 
elasticity is at right angles to the cylinder axis. 
From what has been shown as to the complex structure of 
outer segments, their delicacy and sensitiveness to slight 
stimulation, I think it will be unnecessary to try further to 
disprove the view that they are cuticular in nature or even 
secretions (pp. 567-568). Nor is there any good reason for 
considering the outer segment non-nervous, for, as I have 
shown, the fibrils run the whole length of the visual cell, 
and these fibrils satisfy well the conditions which Schultze 
('72a;"7oab. p. 827) leoked tor when he wrote:,. atone 
time believed it possible to point out the way in which the 
outer segment might take a share in the act of perception, 
namely, by means of the fibers, discovered by me, which run 
over the surface of the inner segment and are continued upon 
the outer segment.” 
Having considered the characters of the outer segment, we 
may now take up the cell organs of the inner segment, 
treating of them in the order of their occurrence from the 
distal to the proximal end. 
The intermediate plate, which has been observed in a 
number of forms, may be of more general occurrence than 
has been reported. Its small size would account for its having 
been overlooked, though it is usually differentiated clearly. 
The plate-like form and the fact that staining fibrils* pass 
over its edge only, and not through it, suggest an isolation 
function between inner and outer segments. Greef (: 00) 
applied the name “Zwischenscheibe” to it, supposing that the 
structure had not been previously described; but from a glance 
* Fibers which Schultze finally concluded were from sustentative tissue 
(Schultze, 72b, p. 823). 
