168 



said that the Chologaster did not change because it prob- 

 ably 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 Cyprino- 

 dontes, 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 Typhlichthys in the 

 same waters? To assume, that under the same conditions, 

 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 under- 

 stand them. 



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 subterra- 

 nean streams, was a salt and brackish water estuary, inhab- 

 ited 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 numer- 

 ously represented than now, as many probably became 

 exterminated as the salt waters of the basin gradually 

 became brackish and more limited, as the bottom of this 

 basin was gradually elevated, and finally, as the waters be- 

 came confined to still narrower limits and changed from 



"* ' O 



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 Hetero- 



