98 THE MAMMOTH CAVE. 



cranium, from the effects of the alcohol, was 

 such as to render it impracticablcvto 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. 



"Examined 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 continuous 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 



