CHAPTER IIL 
THE BLIND FISHES OF THE MAMMOTH CAVE AND THEIR 
ALLIESA^ 
BY F. W. PUTNAM. 
The blind fish of the Mammoth Cave has Trom its discovery 
been regarded with curiosity by all who have heard of its exis- 
tence, vdiile anatomists and physiologists have considered it as one 
of those singular animals whose special anatomy must be studied 
in order to understand correctly facts that have been demonstrated 
from other sources ; and, in these days of the Darwinian and devel- 
opment theories, the little blind fish is called forth to give its tes- 
timony, pro or con. 
Before touching upon this point, however, we must call attention 
to the structure of the fish and its allies, and to others that are 
either partially or totally blind. 
In the lancelet (Branchiostoma) and the hag (Myxine) the e}^e 
is described ‘^as simple in form as that of a leach, consisting sim- 
ply of a skin follicle f coated by a dark pigment, which receives the 
end of a nerve from the brain.” Such an eye speck as this struc- 
ture gives would only answer for the simple perception of light. In 
the young | of the lampreys (Petromyzoli) the eye is very small and 
* From the American Naturalist for Jammiy, 1872. 
t See farther on where Prof. Wyman questions this structure. 
i These young lampreys have heen described under tiie generic name of Ammocoetes, 
and it was not until 1853, when Prof. Miiller discovered the fact of a metamorphosis in 
the lampreys, that their true position was ascertained. Prof. Miiller has traced the 
history of the common European species and shown that it is three or four years in 
attaining its perfect form. With this fact before us and Vvdth the early stages of the 
Myxinoids still unknown, have we not some reason for suspecting that the Lancelet may 
yet prove to be a larval form of the Myxinoids, notwithstanding that it is said to lay 
eggs ? Why should we not suspect the existence in the very lowest vertebrates of some- 
( 29 ) 
