ORIGIN OF THE BLIND FISHES. 



49 



From this brief comparison of some of the prominent charac- 

 ters of the genera of the Heteropygii with the Cyprinodontes, their 



f Aphredoderus and Gymnotus, and other genera of distinct orders have this forward 

 position of the anus also. 



J The air bladder is in several families present in some species and absent in others. 



The presence or absence of scales on the head, or on portions of it, is a generic 

 character subject to great variation in many families and quite constant in others. 



II I cannot recall anything but the barbels on the head and jaws of many genera of 

 Cyprinoids, Siluroids, Gadoids, etc., etc., that can be said to be tactile organs among 

 fishes, with the exception of the fleshy papillae on the head and body of the blind fishes 

 of the American and Cuban caves, and the filaments of the fin rays of many fishes 

 and the fleshy ventral rays of the Gurnards. 



IT Of all fins, the ventrals are the most likely to deviate from their normal structure 

 and position. Their presence or absence, as exhibited in many families, and often by 

 different ages of the same fish, and the great variation in their ppsition in different 

 genera of the same family, render any change in them of either generic, specific, or 

 individual character, or simply indicative of age (as they are lost in some adult fishes 

 while present in the young, and in others not developed until after the other fins). 



** As I have alluded to the fact, in the first part of this paper, the eyes of fishes are 

 no more the constant and unvarying part of the fish structure than the ventral fins, and 

 like them are subject to almost every conceivable variation in position in the head, and 

 perfection in structure. 



tfThe largest specimen I have seen of Typhlichthys, is less than two inches in length 

 and as the eye of an A^mblyopsis of twice the size is not over a 32d of an inch in width 

 it must be very small indeed in Typhlichthys, and I confess to not being able to find it 

 in an ordinary dissection, assisted only by a good lens. 

 MAMMOTH CAVE. 4 



