CHAPTER XVI 



CIRCULATORY 

 SYSTEM 



An early drawing showing the 

 circulation of the blood. 



Malpighi's drawing of circula- 

 tion of a chick embryo. 



What are the paths of blood through the body ? What causes the cir- 

 culation of blood? What is the relation of circulation to the cells? 



Problem. The study of blood vessels. 



Anaesthetize a tadpole with a little ether. Place the tadpole in a Petri 

 dish in a little water so that the tail can be mounted under the low pow.er 

 of the microscope. Do not keep the tadpole out of water more than ten or 

 fifteen minutes at one time. 



I. Note the blood flowing up some blood vessels and down others. 



A. Suggest a reason for the parallel arrangement of the blood vessels. 



B. Suggest a function of the connecting blood vessels. 



II. The large elliptical cells passing through the vessels are the red cor- 

 puscles. 



A. What is the advantage of having corpuscles in the smallest blood 

 vessels pass cells in a single line ? 



B. Compare the red corpuscles of the frog with those of man. 



III. Look at the sun or at a very bright light. Note tiny particles passing 

 through a network of tubes in your eyes. These are the red corpuscles passing 

 through tiny blood vessels. 



In the plant, a system of tubes called ducts and sieve tubes dis- 

 tributes cell sap. In the human body, a network of tubes makes 

 up the circulatory system for the distribution of blood throughout 

 the body. Materials must enter and leave the blood by means 



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