PISCES 



201 



Excretion,— The nephridea unite in a i^air of large kidneys. 

 The ureter may or may not empty into a urinary l)ladder. 



Circulation (Fig. 160). — The heart is surrounded by a peri- 

 cardium. It consists of simis venosus, auricle, ventricle, and 

 conus arteriosus. The blood, which is red, goes from the gills 

 over the body. The veins collect it and return it to the sinus 



Branchial artery^ 



Arterial bulb ^, 



Ventricle of the heart .^. 



Auricle of the heart — 



Venous sinus--- 



Vena portse, liver, etc.". 



Branchial vessels 



-Dorsal artery 



Kidneys 



Dorsal artery or aorta 



Fig. 160. — The circulatory apparatus of a fish. (Tenney.) 



venosus, from which it passes through the parts of the heart in the 

 order named, and the circulation begins anew. 



Respiration is by gills except in the lung fishes, which take the 

 mechanically dissolved air from the water and give off waste 

 matter. The gills arise as paired pouches of the pharynx and 

 open on the exterior by gill-slits. They are attached to the 

 branchial arches and are persistent through life. 



