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 Paddlefish is allied to extinct ganoid types. 
The group is now represented by one species in 
Amierica and another in central Asia. 
The Sturgeous, 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 (Scaphirhynchus), which 
(like Polyodon) 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 Bow-fins are strictly 
American types allied to extinct ganoid forms, 
and doubtless developed from such in the waters 
they now inhabit. 
The Cat-fishes 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 (Amezurus cantonensis); but 
