14 NATURE OF CELLS 



found. It exists wherever such bocUes of «'ater are found, 

 and, with care, may be obtained for study. 



Structure of the body. — Tlie ))ody of the aniceba is simply 

 a minute mass of semiliquid, colorless protoplasm that 

 has no permanent form because it is constantly changing 

 in outhne and shape. It may contract into a tiny ball, 

 or it may become star-shaped, or it may stretch out 

 and become very thin. 



The protoplasm of the body is granular in structure, is 

 not confined by a wall, and is differentiatetl into two 

 distinct parts, the nucleus and cytoplasm. The nucleus is 

 a light, roundish spot, usually somewhere near the center 

 of the body. The remaining part of the protoplasmic 

 mass, surrounding the nucleus and composing nearly the 

 whole of the body, is the cytoplasm. The outer la>'er of 

 the cytoplasm is somewhat denser and more transparent 

 than the inner part. This bounding layer is called the 

 ectoplasm, while the inner, granular part of the C3'toplasm 

 is called the endoplasm. 



While the body of the amceba is active, slender, finger- 

 like processes of the protoplasm, cahed pseudopodia (Fig. 4), 

 slowly stream out from the bod}^ mass as though they were 

 feelers seeking the way. These pseudopodia are often ex- 

 tenfled and withdrawn without a change in position of the 

 body of the amoeba. Not far from the nucleus is a trans- 

 parent body, which, if watched long enough, will be seen to 

 enlarge slowly and then to discharge its contents suddenly 

 into the surrounding water. This is the contractile vacuole. 



Method of locomotion. — The anuplia has no wings or 

 legs, yet, by watching it closely, it will be found to change 

 its position slowly, and in this way. One .side of the body 

 begins to bulge out, and tliis projection soon develops into 



