THE BLIND FISHES OF MAMMOTH CAVE. vi 
acknowledged nearest allies, we can only trace what could be 
regarded as a transition, or an acceleration, or a retardation of 
development, in simply those very characters, of eyes and ventral 
fins, that are in themselves of the smallest importance in the struc- 
ture (permanence of character considered) of a fish, and, as if to 
show that they were of no importance in this connection, we find 
in the same cave, blind fishes with ventrals and without, and in 
the same subterranean stream, a blind fish and another species of 
the family with well developed eyes. 
If it is by acceleration and retardation of characters that the 
Heteropygii have been developed from the Cyprinodontes, we have 
indeed a most startling and sudden change of the nervous system. 
In all fishes the fifth pair of nerves send branches to the various 
parts of the head, but in the blind fishes these branches are devel- 
oped in a most wonderful manner, while their subdivisipns take 
new courses and are brought through the skin, and their free ends 
become protected by fleshy papilla, so as to answer, by their deli- 
cate sense of touch, for the absence of sight. At the same time 
the principle of retardation must have been at work and checked 
the development of the optic nerve and the eye (which probably 
exists externally in the young fish), while acceleration has caused 
other portions of the head to grow and cover over the retarded eye. 
Now, if this was the mode by which blindness was brought about 
and tactile sense substituted, why is it that we still have Cholo- 
gaster Agassizii in the same waters, living under the same condi- 
tions, but with no signs of any such change in its senses of sight 
and touch? It may be said that the Chologaster did not change 
because it probably had a chance to swim in open waters and 
therefore the eyes were of use and did not become atrophied. 
We can only answer, that if the Chologaster had a chance for 
open water, so did the Typhlichthys and yet that is blind. 
If the Heteropygii have been developed from Cyprinodontes, 
- how can we account for the whole intestinal canal becoming so 
singularly modified, and what is there in the difference of food or 
of life that would bring about the change in the intestine, stomach 
and pyloric appendages, existing between Chologaster and Typh- 
lichthys in the same waters? To assume, that under the same con- 
ditions, one fish will change in all these parts and another remain 
intact, by the blind action of uncontrolled natural laws, is, to me, 
an assumption at variation with facts as I understand them. 
