38 
collapsed so that the ganglionic layer formerly lining the vitreous cavity. 
has been brought together in the center of the eye. 
The layers of the retina in Typhlichthys are so well developed that 
could the vitreous body and lens be added to this eye it would stand on 
a higher plane than that of Chologaster cornutus exclusive of the cones. 
It is generally true that at first the thickness of the layers of the retina 
is increased as the result of the reduction of the lens and vitreous body 
and the consequent crowding of the cells of the retina, whose reduction in 
number does not keep pace with the reduction in the dioptric apparatus 
in total darkness. 
If we bear in mind that no two of the eyes represented here are mem- 
bers of a phyletic series we may-be permitted to state that from an eye 
like that of cornutus, but possessing scleral cartilages, both the eyes of 
Amblyopsis and Troglichthys have been derived and that the eye of 
Amblyopsis represents one of the stages through which the eye of Trog- 
lichthys passed. The eye of Amblyopsis is the eye of C. cornutus minus a 
vitreous body with the pupil closed and with a minute lens. The nuclear 
layers have gone a step further in their degeneration than in cornutus, but 
the greatest modification has taken place in the dioptric arrangements. 
In Troglichthys even the mass of ganglionic cells present in the center 
of the eye as the result of the collapsing after the removal of the vitreous 
body has vanished. The pigmented epithelium, and in fact all the other 
layers, are represented by mere fragments. 
The eye of Typhlichthys has degenerated along a different line. There 
is an almost total loss of the lens and vitreous body in an eye like that of 
papilliferus without an intervening stage like that of cornutus, and the 
pigment layer has lost its pigment, whereas in Amblyopsis it was retained. 
The salamanders bridge the gap existing between the Chologasters and 
the blind members of the Amblyopsidae. But even at the risk of monot- 
onous repetition I want again to call attention to the fact that the sala- 
manders do not belong to the same series as the Amblyopsidae. The 
dioptric arrangements of Typhlotriton are all normal; the retina is normal 
in the young, but the rods and cones all disappear with the change from 
the larval to the adult condition. In Typhlomolge the lens and largely 
the vitreous body are gone and the eye has collapsed. The vitreous body 
is, however, much better represented than in the blind Amblyopsidae and 
the iris is, especially in the young, much better developed than in the 
fishes. ' 
‘ny 
‘ 
