586 HOWARD. [VoL. XIX. 
course of those of the far cone. These relations are made 
clear in cross sections (Pl. 1, Fig. 5, 4.) and different lateral 
views (Fig. 2, 4 and B.). In the preparation represented 
in Figure 2, B, the near cone, being out of focus, is shown 
by dotted outlines only. 
The twin cones possess two nuclei, each element having 
its own, though the two lie in close contact. The nucleus of 
the far cone is like the other nuclei, but that of the near 
cone has a prolongation (Pl. 1, Fig. 2, prc. nl.), which 
reaches beyond the membrana limitans externa into the sheath 
of the paraboloid. Another difference between the two nuclei 
is usually discernible; the nucleus of the near cone (nl. con. 
prx.) contains a fine granulation giving a greyish cast, that 
of the far cone possesses larger, densely staining granules and 
is otherwise more transparent, because of the absence of the 
finer granulation. 
A well defined foot in the double cone is sometimes dis- 
tinguishable (Pl. 2, Fig. 7, pd. con.), the fibrils converging 
and then diverging into the middle of the outer retinular layer. 
From estimates based on the fundus of the retina, the 
relative number of rods, cones, and double cones in Necturus 
are: rods, 4; cones, 1; double-cones, 1. 
A comparison of double-cones with the other elements, when 
stained by Mallory’s (:00) triple stain, brings out some 
interesting differentiations in corrosive-acetic material (Pl. 5, 
Fig. 38). The ellipsoids of the single cones take on a 
brilliant purplish-pink color, while the outer segments take 
a lighter but equally brilliant pink, with the exception of the 
fibrils, which are blue (Fig. 40). The rods also show the 
fuchsin-staining substance, but to a smaller degree, in both 
ellipsoids and outer segments. In the latter it is somewhat 
irregular in distribution, as if extending in the natural state 
throughout the segment, but confined in fixed preparations by 
condensation or contraction to its central portions. In the 
rods, the prevalence of a blue-staining reticulum masks the 
pink somewhat. The mixture of blue and pink in the ellip- 
i 
