CHORDATES IN GENERAL 1()1 



most vertebrates. It secretes the bile and also serves to convert 

 carbohydrates to glycogen (animal starch) to be stored for future 

 energy production. It is also in the liver that protein wastes are 

 converted into urea and uric acid in order that they may be excreted 

 from the blood in the kidneys. The large intestine which is shorter 

 than the small intestine possesses no villi or digestive glands. It 

 receives the fecal matter and delivers it to the anus. The chief 

 function of this entire system is that of dissolving and converting 

 complex food materials into a form which may be absorbed and 

 assimilated by the protoplasm of cells throughout the body. 



The respiratory system is at least in part an outgrowth of the 

 digestive canal. In most aquatic vertebrates respiration is accom- 

 plished by drawing water through gill slits in the wall of the pharynx. 

 Air-breathing, terrestrial forms have developed the trachea (wind- 

 pipe) and lungs as another outgrowth of the pharynx. A certain 

 amount of respiration takes place through the skin. The respiratory 

 process is composed of two phases: external respiration which in- 

 cludes the exchange of the gases, oxygen and carbon dioxide, be- 

 tween the external medium and the blood; and internal respiration 

 which is the exchange of the gases between the blood and the proto- 

 plasm of the cells over the body. Hemoglobin in the red corpuscles 

 of the blood has a loose affinity for oxygen, is capable of carrying 

 it, and then gives it up at points where there is demand for it. 

 Much of the carbon dioxide given up by the cells becomes carbonic 

 acid and carbonates which may be transported by the plasma (fluid) 

 of the blood. 



The circulatory system is a closed system of vessels supplying all 

 parts of the body with blood and a system of spaces, sinuses, and 

 vessels collecting lymph from the various organs to return it to 

 the blood vessels. The blood circulatory system centers in a con- 

 tractile heart from which tubular arieries lead out to various organs 

 of the body where they branch into minute vessels or capillaries. The 

 capillaries converge as they carry the blood away from the organs 

 to form the veins which carry the Wood back to the heart. This is 

 a closed system of vessels. The blood is composed of the clear fluid, 

 plasma, and the hlood corpuscles. The red corpuscles contain the red 

 pigment matter, hemoglobin with oxygen-carrying power. The white 

 corpuscles or leucocytes are of several varieties and they are amoeboid 

 in character. These cells may make their way among cells of , other 



