Phylum Protozoa 359 



In South America, another trypanosome, T. crusi, is transmitted by 

 the bite of a kissing bug. This form causes swelHng in the heart muscle 

 and may be fatal. 



Members of the genus Leishmania also cause human infections. 

 In India and North Africa, kala azar is a common disease in which 

 the liver and spleen enlarge. In Central and South America, L. 

 hrasiliensis causes the disease known as espiindia which afifects the 

 mucous membranes of the mouth, pharynx and nose. All of these are 

 intracellular parasites and are transmitted by the bites of sandflies. 



THE CLASS SARCODINA 



The members of the class Sarcodina vary in appearance from naked 

 bits of protoplasm to forms that are enclosed in elaborate shells. The 

 most commonly studied member of this class is Amoeba proteus. 



Amoeba Proteus. — The individual amoeba consists of a mass of 

 protoplasm surrounded by a cell membrane. The cytoplasm itself 

 consists of two distinct regions : an outer narrow zone of clear, jelly- 

 like protoplasm, the ectoplasm, and the main mass of granular endo- 

 plasm. In the endoplasm are contained the nucleus, food vacuoles, con- 

 tractile vacuoles, and various other cell inclusions. 



The Amoeba moves by means of cytoplasmic extensions, the 

 pseudopodia. These are blunt projections which are thrust out first 

 on one side then on another, resulting in a zigzag forward motion. As 

 the animal moves forward, they again become a part of the main cell 

 mass. Each pseudopodium touches the substratum at its tip, and as 

 the mass of cytoplasm flows forward toward it, the animal moves along. 



Apparently these pseudopodia are formed by colloidal changes in 

 the cytoplasm. The internal mass is in a very liquid state and is known 

 as pla^masol, while an outer narrow portion is denser and more gela- 

 tinous in nature, and is known as plasmagel. At the point where a 

 new pseudopodium will form, the denser gel changes to the more liquid 

 sol by a local chemical reaction. This mechanically causes a flowing 

 forward of the sol of the main mass which by loss of water is changed 

 to a gel around the periphery of the pseudopodium. Thus the indi- 

 vidual pseudopodium consists of a cylinder with a wall of gel, but with 

 the internal protoplasm and the tip in a sol state. This continuous 

 change from gel to sol and back again causes the amoeboid motion. 



These pseudopodia not only serve for the movement of the Amoeba 

 but also serve for the capture of food particles. The food of the amoeba 



