THE BONY FISHES. 155 



cealed spring-trap,, snap together, and the victims are en- 

 gulfed by the dozen. 



But still more useful to the fish in finding their way 

 through the water, and perhaps of use in avoiding their 

 enemies, is the row of touch-organs forming the "lateral 

 line" (Fig. 139, L), which extends from the head to the 

 tail. It is a very delicate apparatus peculiar to fishes and 

 Batrachians. It is sensitive to the faintest movement of 

 the water, enables the fish to notice the slightest displace- 

 ments of water, giving it continual information as to the 

 state of things about it, which its eyes or ears do not afford. 

 This line is governed by the lateral nerve. Among the vari- 

 ous experiments made by a French physiologist, De Sede, 

 to ascertain the use of the lateral line, a barbel was blinded, 

 and, by way of extra" precaution, its barbels were cut off; 

 afterwards its lateral nerve was cut. As long as the fish, 

 even though deprived of its eyes and barbels, retained the 

 lateral nerve it guided itself easily; but as soon as this nerve 

 was severed it remained persistently motionless. In another 

 experiment a perch, blinded and deprived of its lateral line 

 on one side only, was placed in an aquarium divided into 

 numerous compartments; it contrived to keep the unmuti- 

 lated side turned towards any obstacle. 



The bony fishes have also shown great adaptability to dif- 

 ferent and changing surroundings. Of the cod family, the 

 cod lives in deep water, about "banks" or gravelly shoals, 

 or about rocks, while the hake prefers muddy bottoms; the 

 pollock lives in shoaler water nearer shore; on the other 

 hand, the herring and mackerel swim in schools near the 

 surface, devouring the surface-feeding Crustacea, while the 

 members of the flounder family are adapted for swimming 

 close to the bottom, burrowing in the mud after the shell- 

 fish peculiar to such ground. The members of the salmon 

 family have adapted themselves both to the sea and to 

 fresh water; the salmon- and sea-trout live in the sea in win- 

 ter, but ascend rivers to spawn; then there are land-locked 

 salmon-trout, lake-trout, and brook-trout. There are sea- 



