LECTURE VIII. 



JL HE course of our Zoological investigations has 

 now led us to a very extensive tribe of Animals, 

 distinguished by the title of Fishes. Like the 

 Amphibious animals their heart, in the language 

 of anatomists, is unilocular, or consists but of one 

 chief cavity, and their blood is far less warm than 

 that of the higher order of animals, as quadrupeds 

 and birds : the red particles of their blood are also 

 of an oval shape. The organs of breathing in 

 Fishes, analogous to the lungs in quadrupeds and 

 birds, are distinguished by the name of gills, and 

 consist of a vast number of ramifications of blood- 

 vessels, curiously disposed in rows, and supported 

 on a certain number of bony arches, generally 

 four, on each side the breast. By the gills the 

 air contained in the waters they inhabit, is sup- 

 posed to afford oxigen to the blood in its passage 

 through the very delicate ramifications of the 

 blood-vessels on the gills 3 so that the same pro* 



