GENERAL PAET. 



I. Cells and Tissues (Histology). 



The name Protozoa is given to a group of animals of very 

 simple organisation^ whicli form the lowest grade in the animal 

 kingdom. It is well to begin a study of zoology by considering the 

 A m oe b a J one of the many animals belonging to this group^ because, 

 in order to appreciate animal organisms in general, it is extremely 

 important to understand thoroughly a simple creature such as this. 



The Amoeba is a microscopic organism which is frequently found 

 in fresh water. Its shape is irregular and indefinite. It consists of a 

 substance called protoplasm, a finely granular, viscid substance, 

 which, on chemical analysis, is found to consist of a number of difEerent 

 constituents, albumen being one of the most important. Protoplasm 

 also contains a considerable quantity of 

 water and of various other materials. 

 In the protoplasm is a rounded or oval 

 body, the nucleus, and in this again 

 is a smaller spherical body, the nu- 

 cleolus. The Amoeba possesses a 

 number of qualities, the most obvious 

 of which is its power of movement: 

 small processes, called pseudopodia, 

 are thrust out from the surface, by the 

 streaming of part of the general sub- 

 stance of the animal towards certain 

 points ; the pseudopodia then disappear, 



and new ones are formed; but apart from this the protoplasm is in 

 constant motion, as is shown by the way the granules move about. 

 The mobility of the protoplasm gives the Amoeba the power of loco- 

 motion, whereby it can glide through the water, past any given object, 

 with greater or less rapidity. Movements may take place without an 

 external stimulus, they are then said to be spontaneous: in other 

 cases there is such a stimulus ; a movement, often the drawing-in of 

 the pseudopodia, follows contact with some object, but the movement 

 proceeds from the Amoeba itself, it is not directly caused by the 



B 2 



Pig. 1. An Amoeba at two 

 different moments. k nnoleus, 

 V vaouole, n ingested food. — ^After 

 Gegenbanr. 



