PLATE 5. 
(Continued from preceding page.) 
When the sheath is absent the reaction of the axis cylinder is seen to be 
unmistakably the same as that of the outer segments of the rods; 7. e., 
the longitudinal axis is the positive optical direction. 
Ic. 45.—Outer segments of a rod and cones from a Necturus that had 
been kept in the dark three days. The outer segment of the cone gives the 
long axis as the negative optical direction instead of the positive as 
usual. 
Fic. 46.—Diagram showing the polarization color reaction observed 
in the visual rod of the slug Limax maximus. The fibrillar structure 
is shown in black as figured by Dr. Grant Smith (: 06) from a preparation 
fixed in vom Rath’s platino-osmo-acetic mixture. 
