INTESTINAL PROTOZOA, AMCEBA 



227 



or Sarcodina. The members of this order are either naked 

 masses of protoplasm or enclosed in a simple shell, either 

 secreted by the organism or formed from some foreign 

 substance. They have blunt, lobulated or finger-shaped 

 pseudopodia and a single nucleus. Many of them live 

 in fresh or salt water, and are abundant where there is 

 moist decaying vegetation ; some are parasitic. In the 

 genus Amoeba the body is always naked, and usually there 



FIG. 64. Balantidium coli. 



is a marked distinction between the outer part, ectosarc, 

 and the interior, endosarc. The former is clear and 

 transparent but viscid, whilst the latter is more liquid 

 and granular, and frequently contains foreign bodies 

 taken in as food. The compact nucleus and a contractile 

 vesicle are contained in the endosarc. 



When active the amoebae are constantly changing shape, 

 and throw out blunt processes or pseudopodia. The 

 number and shape of these are points to consider in the 

 differentiation of species. When motionless or dead the 



