314 



ANIMALS 



Nucleus 



Cilia 



FIG. 254. Slipper Animalcule (Para- 

 mecium), magnified. View of the 

 Under Side. 



corpuscles, have the form and the simple structure of the ameba; but 

 they are not so active. 



A more highly developed one-celled animal is called the "slipper 

 animalcule," from its shape (Fig. 254). Animalcule (pronounced, 



an-i-mal-kul) means " little ani- 

 mal." The scientific name of the 

 creature is paramecium. In this 

 case the cell has 

 a permanent place 

 for feeding, called 

 the mouth, and the 

 mouth extends in- 

 ward, forming a gullet. The creature has a per- 

 manent shape, because its cell wall is more stiff than 

 that of the ameba. It swims about by waving the 

 thread-like extensions (cilia; cf. 324) of its cell wall. 

 A third one-celled animal is called vorticella, or 

 the "bell animalcule" (Fig. 255). Its shape is like 

 that of a bell with a long handle. It is called vor- 

 ticella because, by waving the cilia at its mouth, 

 it produces a vortex, or whirlpool, by which food 

 is carried into the cell. The cell wall is ex- 

 tended to form a "stalk," by which the creature 

 attaches itself to weeds, or to sticks and stones 

 in the bottom of ponds. 



FIG. 255. Bell Ani- 

 malcule (Vorticel- 

 la), magnified. 





334. Simple Many-Celled Animals ; 

 Hydra. If a water plant is placed in 

 a glass vessel of water, a hydra (Fig. 

 256) is often found attached to the 

 plant or to the sides of the vessel. 

 It is a brown or greenish creature half 

 an inch long, or less. 

 When it is not disturbed, the hydra extends several 

 thread-like "arms," called tentacles, about in the water. 



FIG. 256. Hydra, or Polyp. 

 Exterior View and Cross 

 Section. Magnified. 



