No. 3.] VISUAL CELES IN VERTEBRATES. 617 
the rod foot it is very evident that they diverge into the outer 
reticular layer. If the fibrils came from the ‘‘fiber basket”’ 
and belonged to the Muller’s fibers, or sustentative cells, 
they would in general converge toward the nuclei of these 
cells located in the middle nuclear layer. Instead of this, 
the fibrils in question diverge on leaving the foot process of 
the visual cells. 
Verheeff (:03) contends, with good reason, that the old 
idea that the membrana limitans externa is made up of the 
external end of the Muller’s fibers, is incorrect. He finds 
a fenestrated membrane in the pigmented epithelium almost 
identical with the membrana externa, and argues that since this 
cannot be produced by Muller’s fibers the probability is against 
that being the case in the membrana limitans externa. He finds 
these fenestrated, net-like membranes present generally in epi- 
thelia and believes they are produced by the epithelial cells them- 
selves. Schneider (: 02) describes in epithelia what are prob- 
ably identical structures as “Schlussleisten’”’ and ‘“Desmochon- 
dren.” I have examined Dr. Verheeff’s excellent preparations 
of the human retina, in which this fibrillar membrane shows 
distinctly. I had previously seen the same in the pigmented 
epithelium of teleost retinas and puzzled over its meaning. 
Retzius (:05), however, shows in the pigment epithelium of 
the dogfish sustentative cells producing long intercellular fibrils. 
If such elements are generally present in retinal pigmented 
epithelia, Verhceff’s opinion would be somewhat discredited. 
However, Verhceff states that such are not present in man. 
By Cone Cenis: 
Every indication points to a complex structure in the 
outer segments of cones and, because of their instability, to a 
more difficult problem than in the corresponding part of the 
rod. This peculiarity, making it difficult to obtain outer 
segments of cones in the fresh condition, accounts probably 
for the absence of reports as to their double refraction. That 
