Protozoa. 293 



There is also a rather distinct layer, or cuticle, forming 

 the outer layer of the ectoplasm. The whole surface 

 is covered with small, hairlike projections called cilia. 

 These are prolongations of the protoplasm which makes 

 the body of the paramecium. These have the power of 

 actively lashing back and forth, acting like so many pad- 

 dles, by means of which the paramecium swims. At the 

 more pointed end, usually kept in the rear, there is a 

 bunch of longer cilia, which seem to serve as a rudder. 

 Sometimes the animal reverses its direction and proceeds 

 with the pointed end foremost, but ordinarily only for a 

 short time, to back out of a tight place and to get a new 

 start in another direction. 



How Paramecium Eats. Along the flat surface is a 

 groove, which at one end forms a blind passageway dip- 

 ping into the body. Both the groove and the tube, which 

 is a gullet, are lined by cilia. By their vibrations these 

 cilia collect small one-celled plants and animals, or other 

 particles of organic matter, which accumulate at the inner 

 end of the gullet. From time to time -this inner end is 

 cut off by constriction, and a collection of food particles, 

 with some water, is pushed into the soft protoplasm of 

 the body. It then is what is termed a food ball, or some- 

 times the space with its contents is designated a food 

 vacuole. These food vacuoles may be regarded as so 

 many improvised stomachs. The masses slowly rotate 

 around in the body in the manner indicated by the arrows 

 in the accompanying figure. At a point about opposite 

 their starting-point any undigested residue is expelled 

 through a weak place in the wall, there being no permanent 

 anal opening. 



Excretion in Paramecium. There are usually two clear 

 spaces in a paramecium, one near each end. These may 



