100 SCIENCE SKETCHES. 



relatives. Still others are evidently modified im- 

 portations from the sea; and of these some are 

 very recent immigrants, landlocked species which 

 have changed very little from the parent stock. 



The character and possible origin of each of the 

 thirty-four families of North American fresh-water 

 fishes may be briefly summarized as follows : — 



The Lampreys are evidently of marine origin, as 

 the marine species are still anadromous. The 

 fresh-water species, compared with the marine 

 ones, are smaller in size and weaker in organiza- 

 tion, and represent larval conditions or arrests of 

 development of the latter form. 



The Paddle-fish is allied to extinct ganoid types. 

 The group is now represented by one species in 

 America and another in central Asia. 



The Sturgeons, like the Lampreys, are anadro- 

 mous. But two of the American species are now 

 confined to the fresh waters, and one of these be- 

 longs to a peculiar genus (^ScaphirhyncJms^ , which 

 (like Polyodoii) has representatives also in central 

 Asia. As to whether the parent stock in either 

 case is American or Asiatic, I know of no positive 

 evidence. 



The Gar-pikes and the Bozv-fins are strictly 

 American types allied to extinct ganoid forms, 

 and doubtless developed from such in the waters 

 they now inhabit. 



The Catfishes of America are all probably de- 

 scendants of a common stock, not allied to South 

 American forms, but probably finding its nearest 

 relatives in India. A single species of this type 

 now exists in China {Ameitims eantonensis') } but 



