No. 3.] VISUAL CELLS IN VERTEBRATES. 593 
(b) CONEs. 
The outer segments of the cones in Necturus are very 
difficult to observe in the fresh state, because of their dis- 
tortion and dissolution immediately after death. Individual 
cases, however, may sometimes be found which preserve a 
constant form long enough to permit of observation and 
even of drawing with a camera lucida (Pl. 2 ioe 0) ee laa 
Necturus the marked conical form of the outer limb and differ- 
ences in the ellipsoid make them readily distinguishable 
from the rods. The dissolution, so far as there is any reg- 
ularity in it, usually results in an elongation of the cone (PI. 3, 
Fig. 22) combined sometimes with a spiral twist. While still 
intact the appearance of the cone is like that of the outer seg- 
ment of a rod, but less refractive. I have not observed an 
intermediate plate in the case of the cones. 
The other portions of the cone appear like the corresponding 
parts of the rod, except that the ellipsoid of the cone is longer 
and the paraboloid is usually not in contact with the nucleus. 
Figures 1 (Pl...) and 20 (PI. 3) give a fairer idea of the 
usual form than the fresh cone shown in Figure, 10, (Pl o2)y, 
as the latter is abnormal. 
2, In Polarized Light. 
During my studies on fresh material the question arose, 
whether there were not some means of making visible in the 
fresh elements structures which the inspection of fixed prep- 
arations led me to believe to be present in the living rod. 
Such a method, if found, must be in the nature of a variation 
in the light used. Polarized light seemed to offer the method 
desired, since, as is well known, some transparent bodies of 
similar appearance in ordinary light are brought out in strong 
contrast when seen under a polarizing microscope. Again, 
organic bodies of a fibrous structure give a definite reaction 
by this method and the direction of the fibrils seems to deter- 
mine the result, since the color reaction is constant for a given 
direction. 
