PROTOZOA 



127 



The activities of a protozoon may be considered under LOCOMOTION, 



METABOLISM* and REPRODUCTION. 



LOCOMOTION. The protozoa have several different modes of mov- 

 ing themselves about. Some of them move by the formation of 

 temporary processes or pseudopodia; in 

 this method of progression, the protoplasm 

 flows out, in finger-like processes, from the 

 body of the organism and, as the protoplasm 

 flows into these processes, the whole organ- 

 ism progresses, literally, by flowing along. 

 Some of the gregarines move about by 

 means of a flowing of the protoplasm which 

 always takes place in one direction; it is 

 probable that |the control of the direction 

 of the flow in these parasites is effected by 

 the contraction of myonemes. These are 

 contractile fibers, which usually lie near the 

 surface of the organism possessing them. 

 Through their contraction, the form of the 

 body of the parasite may be altered and, in 

 this way, motion may be produced. Cilia 

 are small hair-like processes, which may 

 occur either in definite areas or in large 

 numbers over the whole surface of a proto- 

 zoon. They produce motion by waving 

 and, acting together, make a strong simul- 

 taneous stroke in one common direction, 

 ic movement of all the cilia of an organ- 



jm is, however, usually not synchronous 

 >ut proceeds in waves across the surface 

 >f its body so that the appearance is simi- 



ir to that produced when a breeze passes 



:ross a field of grain. Flagella are larger 



tan cilia; they are whip-like processes 



rhich have a lashing movement. They 



ire usually few in number and are often placed at the ends of the or- 



inism. Undulating membranes consist either of a thin fold of the sur- 

 layer or of rows of fused cilia and form either fin-like organs ex- 



*(Seep. 195.) 



cv.'- 



FIG. 92. Paramecium 

 caudatum: division showing 

 the macronucleus (N) divid- 

 ing without mitosis, the mi- 

 cronucleus (ri) dividing mi- 

 totically. c.z>i.,Old, andc.v 2 ., 

 new, contractile vacuoles. 

 (Minchin, after Butschli and 

 Schewiako/, in Leuchart 

 and Nitsche's Zoologische 

 Wandtaflen, No. LXV.) 



