50 . ORIGIN OF THE BLIND FISHES. 



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 s}^stem. 

 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 subdivisions take 

 new courses and are brought through the skin, and their free ends 

 become protected by fleshy papillae, 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, while accelera- 

 tion 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 Typhlichtlrys 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. 



