No. 3.] VISUAL CELLS IN VERTEBRATES. 565 
the relation of the lenses in a compound achromatic objective, 
a proximal bi-convex body fitting into a distal plano-concave 
one. In osmic acid the plano-concave body is colored brown 
like the ellipsoid in other forms, and it also becomes dark red 
with fuchsin. On the other hand, the bi-convex body stains 
like the remainder of the inner segment. This body was 
called the “paraboloid” by Krause. In the fresh condition the 
plano-concave part, or ellipsoid, is finely granular, while the 
paraboloid is completely homogeneous. According to Max 
Schultze the paraboloid may be isolated. 
The channeling of the outer surface of the inner segment, 
as reported by Merkel (’70), was not credited, and another 
question in dispute was the presence or absence of a membrane 
enveloping the segment. Landolt (71) and Merkel reported 
its presence, while Max Schultze claimed that there Was no 
distinct membrane, but that fibrous projections from Miiller’s 
fibres extended over the inner segment and the proximal third 
of the other segment. Schultze was at one time disposed to 
consider these as nerve fibrils, but was led finally to the view 
last given. He says (’72b, p. 823): “Although the fine fibres 
are with difficulty traced backwards into the external granule © 
layer, I have ascertained this much with certainty, namely, 
that they are continuous with the tissue lying between the 
fibres of the rods and cones. But since this tissue can only be 
considered as connective substance, the fibrils in question rep- 
resent a continuation of the delicate fibrillated connective sub- 
stance of the external granule layer, and form supporting 
fibrillar framework for the bases of the rods and cones (Comp. 
nies 26) 4 
The Cones have parts corresponding to those in the rods, 
and these parts in general show similar reactions both to 
chemical reagents and to light. In amphibians the difference 
between the other segments of the rods and cones in these 
respects is less marked. The conical outer segments possess 
channeling of the outer surface, as in the rods, but with 
grooves nearer together. The outer segments of the cone are 
