ORIGIN OF THE BLIND FISHES. 51 



Looking at the case from the standpoint which the facts force 

 me to take, it seems to me far more in accordance with the laws of 

 nature, as I interpret them, to go back to the time when the 

 region now occupied by the subterranean streams, was a salt and 

 brackish water estuary, inhabited by marine forms, including the 

 brackish water forms of the Cyprinodontes and their allies (but not 

 descendants) the Heteropygii. The families and genera having the 

 characters they now exhibit, but most likely more numerously rep- 

 resented than now, as many probably became exterminated as the 

 salt waters of the basin gradually became brackish and more lim- 

 ited, as the bottom of this basin was gradually elevated, and 

 finalty, as the waters became confined to still narrower limits and 

 changed from salt to brackish and from brackish to fresh, only 

 such species would continue as could survive the change, and they 

 were of the minnow type represented by the Heteropygii, and per- 

 haps some other genera of brackish water forms that have not 

 yet been discovered. 



In support of this hypothesis we have one species of the family, 

 Chologaster cornutus, now living in the ditches of the rice fields of 

 South Carolina, under very similar conditions to those under which 

 others of the family may have lived in long preceding geological 

 times ; and to prove that the development of the family was not 

 brought about by the subterranean conditions under which some 

 of the species now live, we have the one with eyes living with the 

 one without, and the South Carolina species to show that a sub- 

 terranean life is not essential to the development of the singular 

 characters which the family possess. 



That a salt or brackish water fish would be most likely to be 

 the kind that would continue to exist in the subterranean streams, 

 is probable from the fact that in all limestone formations caves 

 are quite common, and would in most instances be occupied first 

 with salt water and then brackish, and finally with fresh water so 

 thoroughly impregnated with lime as to render it probable that 

 brackish water species might easily adapt themselves to the 

 change, while a pure fresh water species might not relish the solu- 

 tion of lime any more than the solution of salt, and we know how 

 few fishes there are that can live for even an hour on beino- 



Of 



changed from fresh to salt, or salt to fresh, water. We have also 

 the case of the Cuban blind fishes belonging to genera with their 

 nearest representative in the family a marine form, and with the 



