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 Rays. 
{[V. 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. - 
SubB-cLAss II.—CyYcLostomt. 
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 Myxinide—is entirely marine, the other—the Petromyzontidee—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. | 
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Fig. 11.—Movuru or 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 
439 | 
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