THE SLIPPER ANIMALCULE. 19 



gum solution, and covered. 1 Use low power at first, and 

 make a general survey of the contents of the drop. Sev- 

 eral kinds of animalcules may be present. The slipper 

 animalcule (Paramecium) may be recognized by its elon- 

 gated, somewhat slipper-shaped form, and by its rapid pro- 

 gression with one end always forward. 



Study its actions. Observe that paramecium, unlike 

 amoeba, when it reverses its direction of travel, turns 

 around ; that it has anterior and posterior ends. Yet it 

 can and does move backward when cornered, as may be 

 seen when one swims into a narrow space between two 

 cotton fibers, and has to batik out. 



Find one that may be retained within the center of the 

 field, and examine it, magnified 300 to 500 diameters. 

 Observe : 



1. That paramecium has a definite, permanent, though 

 unsym metrical shape. 



2. That its body is a single minute mass, without par- 

 titions or divisions ; i.e., that it is a single cell. 



3. That its body mass is made up of two layers, 

 (#) An outer, transparent ectosarc. 



(6) An inner, granular, and more fluid endosarc. 



4. That the whole body is covered over with delicate, 

 transparent processes, shaped somewhat like eyelashes, and 

 hence called cilia. In an active paramecium, these cilia are 

 moved so rapidly, they may be seen but dimly, like the 

 spokes of a rapidly revolving wheel. It is by means of 

 these cilia that the paramecium swims. They are used as 

 a boy's arms are used in swimming : they are struck back- 

 ward quickly and forcibly, and are drawn forward again 

 more slowly. It must be noted that they are not hairs, 

 but only delicate projections from the body wall. 



Observe also, focusing up and down to bring into view 

 the parts at different levels, 



1 See Appendix, p. 279. 



