PISCES 



201 



Excretion. The nephridea unite in a pair of large kidneys. 

 The ureter may or may not empty into a urinary bladder. 



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

 cardium. It consists of sinus 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 portae, liver, etc. 



Intestim 



Vena cava' 



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. 



