THE OPTIC LOBES AND OPTIC TRACTS OF AMBLY- 
OPSIS SPELAWUS DEKAY.? 
By Eart E. Ramsey. 
With Plates III and IV. 
Amblyopsis spelzus is one of the blind fishes inhabiting 
the caves of the Ohio Valley. It is occasionally found in Mam- 
moth Cave and in the surrounding caves. It is locally abun- 
dant in the caves north of the Ohio River. The specimens 
examined were taken near Mitchell, Indiana. 
The eye of Amblyopsis, according to Eigenmann (Roux- 
Archiv, VIII) is a mere vestige. It is a solid ball of cells with 
no vitreous body and probably no lens, with the ganglionic 
layer forming a solid funnel-shaped mass of cells passing through 
the center. In the adult, the optic nerve has not been success- 
fully traced to the brain either by dissections or by means of 
sections. What is left of the optic nerve in the adult forms a 
~ flocculent strand of tissue that can be followed but a short dis- 
tance beyond the eye. Amblyopsis passes its entire life 
in total darkness. It is extremely doubtful whether light im- 
pressions could be received by the eye and transmitted to the 
brain, even ifadult Amblyopsis should be brought to the light. 
However that may be, it seems quite certain that the specimens, 
whose optic lobes served as the basis of this paper, had spent 
their lives in the caves and their optic lobes had no opportunity 
of functioning as the central organ of sight, even if there is a 
nervous connection with the eye. 
A comparison of the macroscopic appearances of the brain 
of a normal fish and that of the blind fish, Amblyopsis spelzeus 
Dekay, discloses a number of interesting conditions. The optic - 
lobes and the optic tracts are measurably degenerate. The 
1 Contributions from the Zoological Laboratory of the Indiana University, 
No. 44. C. H. Eigenmann, director, 
ee ee eee 
SS Pe ee ee 
ae ie ee eh 
j 
ee a a 
