EXPLANATION OF FIGURES. 
A.—I. Diagrams of the eyes of all the species of the Amblyopsidae 
and of Typhlomolge. 
A—C, the eyes of Chologaster cornutus, papilliferus and agassiz1i 
drawn to scale. 
D, E, G, H, I are drawn under the same magnification. 
D.—The retina of Chologaster cornutus. 
E.—The retina of Chologaster papilliferus. 
F.—The eye of Typhlomolge under lower magnification. 
G.—The eye of Typhlichthys subterraneus. 
H.—The eye of Amblyopsis spelaeus. 
I.—The eye of Troglichthys rosae. 
The most highly developed eye is that of Chologaster papilliferus. The 
parts of this eye are well proportioned, but the eye as a whole is small, 
measuring less than one millimeter in a specimen 55 mm. long. The pro- 
portions. of this eye are symmetrically reduced if it has been derived from 
a fish eye of the average size, but the retina is much simpler than in such 
related pelagic species as Zygonectes. The simplifications in the retina 
have taken place between the outer nuclear and the ganglionic layers. The 
pigment layer has not been materially affected. These facts are exactly 
opposed to the supposition of Kohl, that the retina and the optic nerve are 
the last to be affected and that the vitreous body and the lens cease to 
develop early. In Chologaster papilliferus the latter parts are normal, 
while the retina is simplified. That the retina is affected first is proved 
beyond cavil by Chologaster cornutus. The vitreous body and the lens are 
here larger than in papilliferus, but the retina is very greatly simplified. 
Cornutus, it must be borne in mind, lives in the open. The eye of the cave 
species Chologaster agassizii differs from that of papilliferus largely in 
size. There is little difference in the retinas except the pigmented layer, 
which is about 26 per cent. thinner in agassizii than in papilliferus. 
There is a big gap between the lowest eye of Chologaster and the 
highest eye of the blind members of the Amblyopsidae. The lens in the 
latter has lost its fibrous nature and is merely an ill-defined minute clump 
of cells scarcely distinguishable in the majority of cases. The vitreous 
body of the latter species is gone with perhaps a trace still remaining in 
Typhlichthys. With the loss of the lens and the vitreous body the eye 
