FISHES 



117 



liver large or small? Simple or lobed ? 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 coloured figure 4.) 



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

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

 d, small intestine; md, large intestine; «,vent; s, s, swim bladder; ni,ni, kidney; hi, 

 ureter; hb, bladder; ro, eggs (roe); mhe, 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. 



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

 carp? (Fig. 220.) Is it above or below the centre 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 

 j ust behind the opening from the ovary. (Coloured 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 



