THE ROOT-FOOTED GROUP THE AMCEBAS 3527 



quently there are several food balls in the body of the animal. The food can be 

 taken in, and the remains ejected at any point, but the latter frequently appear to 

 be cast out at one spot behind the nucleus and contractile vacuole. The animal re- 

 produces by dividing into two halves, each containing a portion of the original 

 nucleus and a contractile vacuole, and each growing to the size of the original. A 

 unit particle of protoplasm capable of carrying on the functions of life, namely, nutri- 

 tion and reproduction, is termed a "cell." Formerly, a unit of this nature was sup- 

 posed to be a sac or vesicle, hence the name "cell," which is retained, though many 

 cells are solid and without a definite wall. The Protozoans are animals consisting of 

 a single cell, or colonies of cells. In the latter case each cell is more or less inde- 

 pendent of the others, and capable of carrying on all the functions of life. All animals 

 above the Protozoa are composed of many cells united into a whole, in which there 

 arises the principle of division of labor. 



The Protozoa are divided into groups, the Rhizopoda and the Infusoria; in the 

 former the body substance is of more or less uniform consistence, and can extend 

 itself from any part of the surface in the form of pseudopods; whereas, in the latter, 

 the outer layer is firmer and denser than the inner, and the animal has a more or less 

 definite shape. In place of pseudopods, the Infusoria develop on their surface one 

 or many fine processes in the shape of cilia or flagella, which set up food-carrying 

 currents, converging toward a definite mouth, and which enable the animals to move 

 rapidly about, when they are not fixed. 



THE ROOT-FOOTED GROUP Class Rhizopoda 



The simple organisms of this class take their name from their power of pro- 

 truding from the body the processes known as pseudopodia, which are often branched 

 like roots of a tree, and by means of which they creep about. The group includes 

 the amoebas, the foraminifers, the sun animalcules, and radiolarians. In the first 

 the pseudopodia are simple and lobose; in the second they are slender, confluent, 

 and reticulate; while in the last two they are simple, radiating, and somewhat 

 stiff. 



THE AMCEBAS Order LOBOSA 



The chief characteristic of this group consists in the usually broad lobose 

 simple form of the pseudopods, which flow out from the body in the shape of finger- 

 like processes. The simplest forms are apparently without even a nucleus, and on 

 this account have been separated from the rest as the Monera. As the first repre- 

 sentative of the group, we may take the form known as Protomyxa, which forms 

 minute orange-colored particles of jelly creeping over shells, and consists simply of 

 protoplasm containing granules, oil globules, and food particles. Occasionally 

 a specimen retracts all its pseudopodia, some of which are broad and others slender, 

 and becomes a quiescent sphere, the contents of which break up into numerous 

 portions, each of which forms a new individual. The amoebas are divided into two 



