98 THE MAMMOTH CAVE. 
cranium, from the effects of the alcohol, was 
such as to render it impracticable to ascertain 
the mode of connection of the optic nerve with 
the optic lobes. A few muscular fibres were 
traced to the immediate neighborhood of the 
eye, and even in contact with it, but were not 
ascertained to have that regular arrangement 
which is seen in the more completely formed 
eyes of other fishes. 
“Hxamined under the microscope with a 
power of about twenty diameters, the following 
parts were satisfactorily made out: first, ex- 
ternally an exceedingly thin membrane, which 
invested the whole surface of the eye, and _ 
appeared to be contimuous with a thin mem- 
brane covering the optic nerve, and which was 
therefore regarded as a sclerotic; second, a 
layer of pigment-cells, for the most part of a 
hexagonal form, and which were most abun- 
dant about the anterior part of the eye; third, 
beneath the pigment a single layer of colorless 
cells, larger than a pigment-cell, and each cell 
having a distinct nucleus; fourth, just in front 
of the globe a lenticular-shaped, transparent 
body, which consisted of an external membrane 
containing numerous cells with nuclei; this 
lens-shaped body seemed to be retained in its 
