162 THE FISH AND FROG 



Observations. — Push a blowpipe down the gullet, into the 

 baglike stomach. Then follow the folded intestine until it reaches 

 the anus or vent, where the solid waste leaves the body. Find, 

 partly covering the stomach, a large lobed gland, the liver. Just 

 above the stomach you will find the ovary or spermary, depending 

 on the sex of fish (female or male) . Still more dorsal, find a glisten- 

 ing, thin-walled sac, filled with gases, the air bladder. Close to the 

 backbone will be found the dark red kidney. Make a drawing to 

 show all of these organs in natural position. The heart is found 

 just in front of the stomach. Study it carefully, comparing it 

 with the figure on page 235, Civic Biology. Make out its connec- 

 tion with the gills, the red structure on each side of the fish's 

 head. What use has the heart ? The gills ? Why should blood 

 be sent to the gills? Study a chart of the circulation of a fish to 

 see where blood comes from as it goes to the heart and where it 

 goes to after leaving the gills. 



The complete round of the blood from the heart back to the heart 

 makes up the circulation of blood in the fish. 



Conclusion. — 1. What are the various systems within the body 

 cavity of the fish ? 



2. What do you understand by the circulatory system ? 



Problem 137: To study the skeleton and central nervous 

 system of the fish. (Extra.) 



Material. — Use prepared skeleton or chart. 



Observations. — Notice the column of bones extending from 

 the head into the tail of the fish. This is called the vertebral column, 

 or backbone. Of what advantage to the fish is a series of bones 

 over one bone? 



NOTE. — The central nervous system, consisting of the brain and spinal cord, 

 lies inside this chain of bones. To this central system nerves pass in from the out- 

 side of the body, bringing sensations, while other nerves pass outward to muscles, 

 causing movement. 



Conclusion. — 1. What are the uses of the skeleton to the fish ? 



2. Why is it made of many bones? 



3 . Are there any other bones in the fish ? Where are they located ? 



4. How is the nervous system protected? 



