348 PHILOSOPHY OF ZOOLOGY. 



that the whole gills of a large skate presented a surface 

 equal to 52250 square inches, or equal to the whole exter- 

 nal surface of the human body. 



Any injury received by the gills of fishes, is attended 

 with much pain, and a considerable effusion of blood. 

 Some fishermen seem to be well aware of this last circum- 

 stance, and cut the gills with a knife as soon as the fish is 

 taken. A copious bleeding takes place ; and they find that 

 a fish so killed, will keep much longer in a fresh state, than 

 one on which this operation of bleeding has not been per- 

 formed. 



The number of respirations in a minute is seldom above 

 thirty, or below twenty. In the same individual it is lia- 

 ble to considerable variation, depending on the will of the 

 animal. 



The blood, after being renovated in the gills, is reabsor- 

 bed by a multitude of minute vessels, which unite together; 

 but, instead of returning the blood to a systemic heart, to 

 be afterwards distributed through the body, this aorta ex- 

 ercises that function, and descends along the inferior side 

 of the spine, in a canal fitted for its reception, giving off 

 arteries, during its course, to the adjacent parts. The 

 blood is absorbed again by veins, which have extremely 

 thin coats. These are much larger in their course than in 

 their termination; and form, in different parts of their 

 course, considerable receptacles for blood. 



It was the opinion of RONDELETIUS, that fishes were 

 destitute of KIDNEYS and the bladder of urine ; but the 

 observations of WILLOUGHBY and others have demonstrat- 

 ed their existence. The kidneys of fishes are uniform in 

 their substance, and of a reddish brown colour. They are, 

 in general, long and narrow, and apparently united into one 

 mass. The peritoneum covers their under surface, and 

 they are placed longitudinally under the spine. The ure- 



