THE FISH 159 



Note the main part, the centrum, and the processes ex- 

 tending above and below. Above the centrum find a cavity- 

 formed by two spines which grow together. This cavity 

 is called the neural arch. What do you find in it? 



(4) Below the centrum are the ribs branching out so 

 as to form an arch. This is called the haemal arch because 

 the main artery of the body runs down the vertebral column 

 in it. Draw an end view of this vertebra. 



(5) Remove a vertebra with its processes from the 

 column behind the anal fin. Look carefully for the two 

 arches. Draw (X2). 



(6) These two cavities are in the main the .same in all 

 vertebrates. The neural cavity contains the spinal cord and 

 is enlarged to give place to the brain, while the haemal 

 cavity is enlarged into the visceral cavity which contains the 

 heart and alimentary canal. 



Make a sketch of the skeleton of the fish showing the 

 location of the parts studied. 



Reproduction. — The eggs of fishes are called spawn and 

 are deposited usually once each year. The fish generally 

 seeks a secluded spot in which to place the eggs, but when 

 they are hatched or before, they are used for food by other 

 fishes or even by the one that laid them. To offset this de- 

 struction a fish sometimes lays thousands of eggs. 



(2) Some of the food fishes from the ocean as cod, 

 herring, salmon, often go many miles up the river to spawn. 

 These are breathers of salt water at all other times, and 

 will die if placed in fresh water at any other time than 

 during the spawning season. 



Some of the eels, a class of vertebrates lower than fishes, 

 after hatching, go up the rivers and creeks for hundreds 



