68 THE MICROSCOPE. May 



connects the swimming bladder with the oesophagus. 

 The food of the smelt is composed of small fishes, or, the 

 marine animals. Nereis is commonly found in its stom- 

 ach. The spleen is a dark colored organ lying above the 

 oesophagus and in front of the swim-bladder. 



3. Just in front of and below the liver is the heart. 

 This organ is red in color and has three parts, one auri- 

 cle and ventricle and the bulbus arteriosus. The auricle 

 is thin walled and nearly surrounds the thick walled ven- 

 tricle (Fig. 4). In front of the ventricle is the " bulbus 

 arteriosus'' from which runs the aorta. The aorta goes 

 forward to the gills and sends off a branch to each side, 

 at every pair of gills. The blood passes upward through 

 the gills, and in its passage is aerated. The branches of 

 the aorta running around the gills, form what are known 

 as aortic arches. The blood is gathered at the top of the 

 arches into the dorsal aorta, and by it is distributed 

 throughout the body. The aorta runs along the under 

 side of the back bone to the tail. The small veins col- 

 lect the blood, lead it to the cardinal veins, and by these 

 it is carried back to the heart. There is a cardinal vein 

 on each side of the body. They are divided into two 

 parts, the anterior and posterior cardinals. The anterior 

 cardinal collects the blood from tiie head and parts in 

 front of the heart, while the posterior cardinal collects 

 the blood from the regions back of the heart. The card- 

 inal veins enter the auricle upon the right and left sides. 

 By the contraction of the auricle, the blood is forced into 

 the ventricle, from the ventricle to the bulbus and soup- 

 on another round. 



The portal vein collects the blood from the alimentary 

 system and leads it to the liver. From the liver the 

 hepatic vein takes it to the heart. 



4. The gills are the respiratory organs of the fish. 

 Water is taken into the mouth and passed out through 

 the gills. Some of the oxygen is extracted and supplies 



