158 FEESH-WATEK AQUAEIA. 



these fisli can often be seen clinging in masses with their 

 leech-like mouths to stones, while the rest of their bodies 

 waves Tip and down with the current. The Lamprey is shaped 

 somewhat similar to an eel, being round for about two-thirds 

 the length of its body, when it gradually flattens towards 

 the tail. 



The mouth of this fish is very curious, and something like 

 that of a leech; when open it has been weU described as 

 " circular and terminal, so that the fish appears as if the 

 head had been cut ofE." The lips are fleshy. This mouth, 

 and these lips, and a piston-like tongue, form a kind of 

 powerful sucker, by which the fish is able to cUng firmly to 

 stones, rocks, and the like. On each side of the head there 

 are seven openings in a horizontal line which lead to an equal 

 number of bronchial cells or gills. When the fish is not 



Fig. 109. Lampern, or Eiver Lamprey (Petromyzon fluviatilis). 



clinging to anything with its mouth, water passes through 

 the mouth to the gills; but when the Lampern is adhering 

 to a stone, the water, being unable to enter by the mouth, 

 passes to the gills through these openings in each side of 

 the head. There is a small aperture or hole in the middle of 

 the back of the head just in front of the . eyes : this is a 

 nostril, and water does not pass through it (as some writers 

 say) to the gills when the mouth is fixed to any foreign body. 

 Such a passage of water is impossible, as there is no du-ect 

 communication between the nostril and the gills. The mouth 

 is well provided with teeth. There are neither pectoral nor 

 venti-al fins : there are caudal and dorsal fins of a certain 

 kind, but as they have no rays proper they can hardly be 

 called true fins. The Lampern swims with a lateral undu- 

 latory motion. Where the streams are very rapid, it frequently 

 rests by anchoring itself with its mouth to a stone. When 



