S04t CARTILAGINOUS FISHES. 



stream : .and many porpoises have been taken out of 

 the Thames both above and below London-bridge : the 

 method of doing this is to fire at them from boats every 

 time they raise their head above the stream ; and the 

 body of the fish is no trifling capture, as it yields a 

 considerable quantity of oil, and the lean is said to 

 resemble veal. 



CHAP. III. 



OF CARTILAGINOUS FISHES, AND THE VARIETIES 

 OF THE SHARK. 



WE have seen that fishes of the cetaceous kind bear 

 an internal resemblance to quadrupeds, but those of the 

 cartilaginous are one degree farther removed : the first 

 distinction to be observed between them is their hav- 

 ing gristles instead of bones. The bones of the cetace- 

 ous tribe are exactly like those of the animal race, 

 whilst those of spinous are solid throughout, and have 

 no marrow in the inside. Fishes of the cartilaginous 

 kind have their bones always soft and yielding ; and 

 age, which hardens the bones of other animals, tend3 

 to relax and soften theirs. 



It has been observed that the cetaceous fish had lungs 

 like quadrupeds, and that there was a strong resemblance 

 in every part of their inside. The spinous kind have no 

 lungs to breathe through ; and their cold red blood is 

 circulated by the means of the impulse made upon their 

 gills by the water. Cartilaginous fish unite both these 

 systems in their conformation ; for, like the cetaceous 

 tribes, they have organs of hearing and lungs; like the 

 spinous kind, they have gills, and a heart without a par- 



