FISHES 



117 



liver large or small? Simple orlobed? The spleen {mi, Fig. 220) 

 lies in a loop of the intestine. The last part of the intestine is 

 straight and is called the rectum. Is it of the same size as the 

 other portions of the intestine? The fish does not possess a pan- 

 creas, the most important digestive gland of higher vertebrates. 



Fig. 220. — Anatomy of Carp. (See also colored figure 4.) 



bf, barbels on head (for feeling) ; h, ventricle of heart; as, aortic bulb for regulating flow to 

 gills; vk, venous sinus: ao, dorsal aorta; ma, stomach; /.liver; gb, gall cyst; mi, spleen; 

 d, small intestine; »id, large intestine; a, vent; s, s, swim bladder; ni,ni, kidney; hi, 

 ureter; hb, bladder: ro, eggs (roe\; mke, opening of ducts from kidney and ovary. 



Questions : Are the kidneys dorsal or ventral ? The swim bladder ? Why ? Why is the 

 swim bladder double ? Does blood enter gills above or below ? 



The ovary lies between the intestine and the air bladder. In Fig. 

 220 it is shown enlarged and filled with egg masses called roe. It 

 opens by a pore behind the vent. The silver lining of the body cavity 

 is called the peritoneum. (See Chap. VII. Human Biology.) 



Is the air bladder simple or partly divided in the perch? In the carp? 

 (Fig. 220.) Is it above or below the center of the body? Why? The 

 air bladder makes the body of the fish about as light as water that it 

 may rise and sink with little effort. When a fish dies, the gases of 

 decomposition distend the bladder and the abdomen, and the fish turns 

 over. Why? 



Where are the kidneys? (Fig. 220.) Their ends unite close under 

 the spinal column. The ureters, or tubes, leading from them, unite, 

 and after passing a small urinary bladder, lead to a tiny urinary pore 

 just behind the opening from the ovary. (Colored figure 4.) 



The Circulation. — The fish, unlike other vertebrates, has its 

 breathing organs and its heart in its head. The gills have already 

 been described. The heart of an air-breathing vertebrate is near 



