A SHORT LECTURE ON EI SUES. 4II 



by the shape of their scales, which in such fishes as the perch and 

 most of our fresh water species, are jagged and comb-like along 

 the posterior edge, while in the case of our friend the salmon, the 

 scales are roaud and smooth at the edges, Tlu: sub-class in- 

 cludes about two-thirds of all the fishes, and are the easiest 

 examples for you to study. 



(A) Ganoid fishes are well represented by the gar-pike or bill- 

 fish of the western rivers and the common sturgeon. The main 

 part of this group, though, consists of fossil fishes, which are found 

 in the same rocks from which we get our soft coal. Many of these 

 odd fishes who perished so long ago looked very much like small 

 alligators, and others were like our bill-fishes and fikes. 



To the fourth and highest sub-class belong those fishes like 

 the sharks and rays or skates, that, instead of a bony skeleton like 

 the true fishes, have one of cartilage. The sharks are noted for 

 their ferocity and their insatiable appetite. They abound especially 

 among the coral islands of the Pacific Ocean, where the people 

 spend about as much time in the water as on land. But so ac- 

 customed do they become to them and so fearless, that it is said 

 an Islander does not wait for the shark to rush upon him, but 

 attacks him instead, with only a knife or sharp stick for a weapon, 

 and generally conquers. The sharks are obliged to turn over to 

 seize anything, their mouth being a good ways back from the end 

 of the snout, which gives the swimmer an opportunity to plunge 

 in his knife. All sharks, however, are not so large. The rays or 

 skates, or their cousin the torpedo, are also flesh eaters, but not so 

 fierce as the sharks. They are easy to recognize by their nearly 

 square shape, with the head at one corner and the long tail at the 

 other. The two remaining corners are made by the very large 

 side fins. The many slender bones spreading out like rays from 

 the shoulder to the edge of this fin gives them their first name, 

 but why they are called " skates " I cannot tell. 



Ernest Ingersoll. 



