in the Fish Gallery of the Indian Museum. 27 



beneath the backbone and supplies the whole body with 

 pure oxygenated blood. 



The Gills of the Ruhu exemplify the type of the Sub- 

 class Teleostei. There are four pairs of them, attached 

 to the convexities of the first four pairs of branchial 

 arches, and they lie in a gill-chamber on either side of 

 the pharynx. Each gill-chamber is protected by a 

 gill-cover, and opens into the pharynx by four wide 

 branchial clefts, but opens to the exterior by a single 

 gill-slit. Special processes known as gill-rakers are 

 generally present along the concavities of the branchial 

 arches — especially of the first — to strain the water as 

 it passes from the pharynx into the gill-chamber. 



In the Heart of the Ruhu (Teleostean type) the vent- 

 ricle gives of a single branchial artery, which has the 

 same course and distribution as that of the Sting-ray, 

 but has no muscular pulsatile arterial cone at its base 

 but only a fibrous thickening known as the aortic bulb. 



The mechanism of breathing in Fishes is as follows. 

 Water containing oxygen in solution is drawn into the 

 pharynx either through the mouth alone, or, when 

 spiracles are present, through the spiracles also. The 

 water passes, through the branchial clefts in the walls 

 of the pharynx, into the gill-pouches or into the gill- 

 chamber. There it is acted on by the gills, which 

 exchange their carbonic acid for its oxygen, and thence 

 it flows away through the external gill-clefts or through 

 the gill-slit. 



In the circulation of the blood in Fishes venous blood 

 is carried to the heart whence it is propelled, by the 

 strong pulsations of the ventricle, to the gills, to be 

 arterialized. From the gills the arterial blood flows 

 into the dorsal aorta to be distributed to the body. 



