I02 SCIENCE SKETCHES. 



species still found in the sea along our coasts. 

 Other species are anadromous, ascending the rivers 

 in the spring. 



The Gizzard-shad is indifferently marine, anad- 

 romous, or landlocked, and is still extending its 

 range in sluggish waters through the agency of 

 canals. 



The various forms of Salmonidce abound in the 

 streams and lakes of all northern regions. The larger 

 species are marine and anadromous, the smaller 

 confined to lakes and brooks ; but all seek streams 

 or at least shallower waters for the purpose of 

 spawning. The whole group had probably a ma- 

 rine origin ; the more strictly fresh-water species 

 being, as is usually the case, smaller in size, weaker 

 in organization, and with feebler dentition. It is 

 often assumed that this group has had its origin 

 in the Atlantic ; but whether in America or in 

 Europe, we have no means of inferring. 



The Trout-perch show a curious combination of 

 characters of spiny and soft-rayed fishes. The sin- 

 gle species is probably, as suggested by Agassiz, a 

 relic of an ancient fauna. 



The Blmd-fisJies are also very unique in their 

 organization. Two of the known species have 

 well-developed eyes, and live in lowland streams 

 and springs. Such are doubtless ancestors of the 

 eyeless forms of the cave streams, but the imme- 

 diate progenitors and relatives of these seem to be 

 extinct. They were probably fresh-water rather 

 than marine forms, and of the same general stock 

 as the ancestors of the Killifishes, Mud-minnows, 

 and Pike. 



