NATURAL HISTORY OF ONTARIO FISH. 



The Class of the Fishes is divided by zoologists into six sub-classes, con- 

 taining : 



I. The Lancelet or Amphioxus. 

 II. The Lampreys and Hag-fishes. 



III. The Sharks and Eays. 



IV. The Ganoid Fishes. 



V. The Teleost or Bony Fishes. 

 VI. The Dipnoi or Lung-Fishes. 



Of these the 1st and 3rd are not represented in fresh waters, and need not 

 concern us here. With few exceptions our fish belong to the fifth sub-class. 



SUB-CLASS II. CYCLOSTOMI. 



The fishes that belong to this group are eel-like forms of parasitic habits, 

 attaching themselves by means of their circular mouths to larger fish, of which 

 they suck the blood. Their skeleton differs very much from that of other fish : 

 it consists of a brain-case formed of cartilage, supports for the gills of 

 the same material, and a notochord running underneath the spinal cord. 

 There are no true jaws, nor limbs, nor ribs as in other fish. One of the families 

 the Myxinidse is entirely marine, the other the Petromyzontidse has some 

 fresh-water species. 



They are at once recognized by the circular sucking-mouth (fig. 11), the horny 

 teeth within it, the single nostril on the top of the head, and the separate openings 

 of the seven gill-pouches on each side of the head. 



Fig. 11. MOUTH OF RIVER LAMPREY. (Petromyzon concolor.) 



The only species in Ontario waters is Petromyzon concolor, the Silvery 

 Lamprey, a small species of no economic importance found in the Great Lakes and 

 living partly as a parasite of the lake Sturgeon, to which it attaches itself and forms 



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