Protozoa. 



287 



appearing portion, the nucleus, and occasionally there ap- 

 pears a clear space, the contractile vacnole. 



If the object is an amoeba, it will usually soon betray 

 itself by its motion. First there is a bulging out on one 

 side, and this projection may be prolonged into a distinct 

 lobe, called a pseudopod. The amoeba may form several 

 of these pseudopods at the same time, so that it may have 

 little central body and nearly all of its substance may be 

 in the pseudopods. These pseudopods may be extended 

 and retracted without changing the place of the amoeba. 

 But more often after a pseudopod has been protruded, the 

 rest of the body follows it, seeming to flow into it; by 



FIG. 169. AMCEBA: CHANGES IN FORM, DRAWN AT SHORT INTERVALS. 



repetition of this process the amoeba changes its place, 

 and thus exhibits not only motion, but locomotion. If 

 watched for some time the amoeba may be seen to change 

 its shape considerably and to make slow progress, some- 

 times for a considerable time in the same direction. 



Patient watching may reveal how the amoeba takes its 

 food. If a small plant or animal cell or portion of such 

 matter lies in its way, a pseudopod is pressed against it 

 and it becomes embedded in the endoplasm. With any 

 such food material there is usually taken a small amount 

 of water. The space occupied by the water and absorbed 

 food is called a food vacuole. Usually a number of these 

 food vacuoles may be seen in an amoeba. After a time the 

 water and other matter disappear, having been digested 

 and absorbed and assimilated into the substance of the 



