CHAPTER V 

 A STUDY OF AMCEBA 



The animals that we know best are all comparatively large 

 and have a body composed of many cells. Ordinarily we think 

 of a mouse or a humming-bird as being very small, but in the 

 insect world there are hosts of animals so small that they can 

 hardly be detected without the use of a magnifying lens. Yet 

 even the smallest of them are as giants when compared with 

 any of the one-celled animals, the Protozoa (Gr. protos, first; 

 zoon, animal), very few of which can be seen with the unaided 

 eye. Before the invention of the microscope the Protozoa 

 belonged to an unseen and unknown world. The earliest 

 lenses enabled the observers to see some of the largest of 

 them, and each improvement of the microscope has enabled 

 us to penetrate further and further into this fascinating field. 

 Now we know in detail the structure and life history of many 

 of these almost inconceivably minute animals. 



Most of the Protozoa live in water, but a few live in damp 

 sand or moss, while many live in the bodies of other animals 

 where they may or may not cause serious injury. No moun- 

 tain stream is too pure, no ditch too foul to be the home of some 

 of these simple animals. 



Amoeba. Among the most familiar of these one-celled ani- 

 mals are the Amoebae. They are most easily found in pools of 

 water, either in the slime or ooze on the bottom or in the 

 sediment that has settled on submerged leaves or sticks. If 

 some of this material is collected and poured into a dish of water 

 and allowed to settle for a few hours, Amoebae may usually be 

 found when small drops of the slime are examined on a slide 

 under the microscope. With the low-power lenses they 

 appear as small, semi-transparent, irregular-shaped objects 

 which, if watched carefully, will be seen to move very slowly. 



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