PISCES. S 



numberless branches to the branchiae or gills, on 

 which it is distributed into subdivisions so small as 

 to escape the eye, unless assisted by a glass. The 

 blood is red, and the red particles are not round, as 

 in the Mammalia, but oval as in the Amphibia. 



The gills or branchia3 are seated beneath two 

 large slits or openings on each side the head, and 

 are analogous to the lungs in other animals. Their 

 general form is semicircular, and they commonly 

 consist of four double rows of fringed vascular fibrils 

 attached to four bony arches. The gills are per- 

 petually subject to alternate motion and pressure 

 from the water: they are guarded externally by the 

 gill-covers or opercula, constituting a pair of strong 

 flaps on each side, and which are furnished with a 

 lateral membrane, dilatable at pleasure by a certain 

 number of bony radii or arches, in such a manner as 

 to enable the animal either to open or close the gill- 

 covers. The blood, after being thrown by the heart 

 into the ramifications of the gills, is collected again 

 by a vast number of small veins, somewhat in the 

 same manner as in the Mammalia, but instead of 

 returning to the heart again, these vessels unite and 

 form a descending aorta without the intervention of 

 an auricle and ventricle. 



The absorbent system in Fishes is thus elaborately 

 described by Dr. Monro, who gives the Haddock as 

 a general example. 



On the middle of the belly, immediately below 

 the outer skin, a lymphatic vessel runs upwards 

 from the vent, and receives branches from the sides 

 of the belly and the fin below the vent ; near the 



