CARTILAGINOUS FISHES, 349 



deep, is compensated by that which they themselves 

 experience from the cachalot, or spermaceti whale. 



I will now leave you to reflect on the wondrous 

 works of the Creator, displayed in the cetaceous 

 fishes, and on their utility to mankind, while I employ 

 myself in selecting for your observation a few of the 

 most remarkable of the cartilaginous kiud. For the 

 present I shall therefore beg leave to subscribe my- 

 self, 



Dear Sir, 



Your's, &c. 



LETTER LV. 



" Hisjaws horrific armed with three-fold fate, 

 Here dwells the direful shark." 



VV E have often observed that nature proceeds fey 

 successive gradations, and you must in perusing my 

 last letter haye perceived, that the cetaceous fishes, 

 descend only one step downwards from the quadru- 

 ped race. You will now/find that the cartilaginous 

 kind is still farther removed from that class of ani- 

 mals. 



The leading characteristic that distinguishes this 

 kind of fish is their having gristles instead of bones, 

 and from their pliancy they bcem to have no bounds' 

 set to their dimensions, but are supposed to increase 

 in size as long as they live. 



Cartilaginous iishes seem to constitute the connect- 

 ing link between the cetaceous and the^spi'^us kinds, 

 and to unite some of the principal propertic of both 

 in their conformation. Like the former they have 

 organs of hearing and hm^, and like the latter they 

 have gills, and a heart without a partition. This dcu- 

 ble capacity of breathing is one of the most remark- 

 able features in the history of animated nature, 



They may be in general divided into fut classes, 

 ^rst those of the shark kind, with a body growing less 



