250 
The eye of 7. subterraneus is surrounded by a very thin layer of tissue 
representing the sclera and choroid. The two layers are not separable. 
In this respect it approaches the condition in the epigean-eyed member of 
the family Chologaster. For other reasons that need not be given here, 
it is quite certain that Typhlichthys is the descendant of a Chologaster. The 
intensity of coloration and the structure of the eye are the chief points of 
difference. The eye of ros@ is but about one-third the diameter of that of 
subterraneus, measuring .06 mm. or thereabout. It is the most degenerate 
as distinguished from undeveloped vertebrate eye. The ppint of importance 
in the present instance is the presence of comparatively enormous scleral 
cartilages.* These have not degenerated in proportion to the degeneration 
of the eye and in some cases are several times as long as the eye, projecting 
far beyond it or are puckered to make their disproportionate size fit the van- 
ishing eye. The species is unquestionably descended from a species with 
well-developed scleral cartilages, for it is not conceivable that the sclera 
as found in Chologaster could, by any freak or chance, give rise during 
degeneration to scleral cartilages, and if it did, they would not develop 
several sizes too large for the eye. At present no known epigean species 
of the Amblyopsidz possesses scleral cartilages. The ancestry of rose 
is hence known. Amblyopsis possesses scleral cartilages and the eye of 
rose passed through a condition similar to that possessed by Amblyopsis, 
but the latter species has ventral fins and is hence ruled out as a possible 
ancestor of ros@. The epigean ancestry of Amblyopsis is also unknown. 
The ancestry of Typhlichthys being quite distinct from that of ros@, the 
latter species may be referred to a new generis named Troglichthys. 
Judging from the degree of degeneration of the eye Troglichthys has 
lived in caves and done without the use of its eyes longer than any other 
known vertebrate. (Ipnops being a deep-sea form is not considered.) More 
than this, ros@ is probably the oldest resident in the region it inhabits. 
Since the specimens kindly sent by Mr. Garman, in the course of ex- 
amination, have been reduced to sections, the specimens now in my pos- 
session, together with a few sent to the British Museum, all having come 
from the same cave, may be considered typical. 
In addition to the acknowledgments made before I wish also to thank 
the officers of the Louisville and Nashville R. R. for transportation to 
Mammoth Cave. I must especially express my appreciation of the assist- 
“Kohl mistook the nature of these structures, as he did of every other connected with 
these eyes, except the lens and ganglionic cells, 
