The Soft-finned Teleostei 353 



like envlronally modified groups above named, the air- 

 bladder shows all stages of reduction to almost complete 

 absorption. 



The above brief study of three important teleostean 

 families and their near allies, brings before us nearly 4000 

 species, that were evidently wholly freshwater in ancestry, 

 and are almost wholly freshwater still. Furthermore it 

 has been noted that when offshoots have migrated either 

 into brawling mountain streams or oceanward, marked 

 morphological modification on the average structure of 

 each of the three groups has occurred. And not least in all 

 three when suth happened, steady reduction almost or 

 quite to the absorption of the air-bladder — a striking here- 

 ditary structure derived from ganoid and even more re- 

 mote ancestry — has been effected. 



Now were we to find, either in the fossil state, or in 

 the living state at present, even a .few primitive marine 

 representatives, that morphologically might serve as the 

 starting point for origin of those now swarming in lakes, 

 swamps and rivers of four continents, a slight basis would 

 exist for possible acceptance of the view that all originated 

 in the sea, and had gradually invaded inland waters. In- 

 stead of this the converse is true, where, as amongst a few 

 of the Siluridae, marine genera or species are encountered. 

 These are clearly derivative and evolved marine members, 

 alike morphologically and distributionally, from the inland 

 forms. 



Again all facts of distribution — botanical as well as 

 zoological — emphasize the existence, in former geologic 

 periods, of extensive land-connections that are now sund- 

 ered. The acceptance of such connections, in correlation 

 with the gradual spread over them of species, genera, and 

 families of freshwater fishes as well as of other groups of 

 animals, at once affords the key to what otherwise are in- 

 explicable problems. 



So with Sagemehl we accept it that all three families 

 above outlined, were derivative from some "ganoid" an- 

 cestor allied to Amia of freshwater habitat. We would 

 further claim that by direct descent from such, and by 

 gradual migration into wider and wider freshwater areas 



