167 



After reviewing the characters of the allied forms, he 

 concluded his remarks as follows : — 



From this brief comparison of some of the prominent 

 characters of the genera of the Heteropygii with the Cy- 

 prinodontes, their 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 structure 

 (permanence of character considered) of a fish, and, as 

 if to show that they were of no importance in this con- 

 nection, we find in the same cave, blind fishes with ven- 

 trals and without ; and in the same subterranean stream, 

 a blindfish 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 Cyprin- 

 odontes, 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 blindlishes these branches are developed 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 delicate 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 acceleration has caused other por- 

 tions 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 Qhologaster Agassizii in the same waters, 

 living under the same conditions, but with no signs of any 

 such change in its senses of sight and touch? It may be 



