THE FISHES OF MINNESOTA. 



KEY TO THE CLASSES. 



A. No paired fins; skeleton not well developed; month a sacking 



disk without jaws. . . (Lampreys.) MarsipobrancLii, 8* 



A A. Faired fins and bony skeleton well developed. (Trne fishes.) Pisces, 10 



Claas MARSIPOBRANCHII. The Lampreys. 



Order HTPEBOARTII. 



Family PETROMYZONID Jl. The Lampreys. 



According to Theodore Gill the lampreys are not included with 

 the fishes, but are placed in a separate class, differing from the true 

 fishes in having very rudimentary skeletons. The body is long and 

 eel-shaped; mouth somewhat circular and beset with horny teeth 

 which point towards the center. On each side of the body just back 

 of the head are seven small, circular holes, the gill openings. There 

 is but one nostril, and that is located on the top of the head just in 

 front of the eyes; dorsal fin notched; a spiral valve in the intes- 

 tine. The young of the lamprey undergo a sort of metamorphosis. 

 Being so different from anything else the lamprey is easily recog- 

 nized. It migrates in the spring with the fishes and is often attached 

 to them. With its sucker-like mouth it can work its way into the 

 body of the fish and may even cause the death of its host. The 

 fish's eye is the part often attacked. 



•These numbers refer to pages. 



