368 The Animal Kingdom 



Paramecium. — As an example of this class, the abundant and 

 familiar Paramecium is usually studied. This animal has a definite 

 body shape and often is called the slipper animalcule due to a vague re- 

 semblance to the shape of a slipper. The anterior end is somewhat 

 blunt while the posterior is pointed. The whole body or cell surface 

 is protected by an elastic covering, the pellicle. Within the cell itself, 

 there is a narrow, clear band beneath the pellicle, the ectoplasm, while 

 the larger mass of the cell is composed of endoplasm with its various 

 inclusions. 



CONTRACTILE 

 \«CUOLE 



MICRONUCLEU! 

 MACflONUCLEUS. 



FOOD VACUOLE 



CAUDAL TUFT 



Fig. 118. — Paramecium caudatum. 



The bases of the cilia arise in the ectoplasm. Each cilium is more 

 or less a modified flagellum, but, of course, much shorter. They cover 

 the entire surface of the body and are more or less arranged in rows. 

 The length of the cilia is quite uniform except for a group of longer 

 ones in the posterior region, the caudal tuft. The individual cilium 

 arises from a basal granule which is connected to other basal granules 

 by an interciliary fibril. This latter acts as a primitive nervous system 

 to coordinate the beat of the cilia. Within the ectoplasm are other 

 structures, the trichocysts. These are spindle-shaped organelles be- 



