MOVEMENT 127 



Euglena, whicli possess chromatopliores and behave like plants, can be 

 grown in distilled water in which certain inorganic salts are dissolved. 

 Saprophytic forms require more complex substances, while holozoic ones 

 will grow only in media in which proteid material is present. This is 

 usually in the form of bacteria, which form the staple food of amoebge, 

 flagellates, and ciliates, when grown on the surface of agar plates or in 

 liquid media. In other cases, as in the cultures of trypanosomes and 

 leishmania, bacteria are absent, the proteid materials being derived from 

 blood-serum. 



MOVEMENT. — The power of movement is one of the properti<^s of 

 cytoplasm in general, and amongst the Protozoa it is seen in its simplest 

 form in organisms like amoebse, and is most highly developed when special 

 motile organs are present, such as flagella, cilia, the contractile filaments 

 in the stalks of the attached Protozoa, and the myonemes of gregarines 

 and other forms. The cytoplasm is in constant movement wathin the 

 organism. This streaming of the cytoplasm is undoubtedly the result of 

 chemico-physical changes which are taking place. In highly-organized 

 Protozoa, like the ciliates, the currents in the cytoplasm are constant in 

 their direction, and the various food vacuoles which move with them 

 perform a definite circuit. In the amoebae, which do not have definitely 

 orientated bodies, there is more irregularity. It is as a result of this 

 streaming of the cytoplasm that organisms like amcBbge are able to move 

 and form pseudopodia. When resting on a surface, the portion of cyto- 

 plasm in contact with the surface is prevented from movement, while the 

 streaming of the internal cytoplasm in one direction leads to a forward 

 movement, which is best illustrated by the roHing movement of a bag of 

 fluid on an inclined plane. In this manner the whole amoeba may progress 

 in one direction, or, when the streaming of the cytoplasm is limited, only 

 portions will move forwards, with the result that pseudopodia are formed. 

 By changes in the direction of the stream the pseudopodia are withdrawn 

 and others protruded. Certain pseudopodia, like those of Heliozoa, are 

 supported by axial fibres, which render them more permanent structures. 

 They are, nevertheless, capable of performing swinging or bending move- 

 ments. Whether these are the result of movements of the cytoplasmic 

 covering or of the axial fibre has not been satisfactorily determined. 

 As, however, fine pseudopodia devoid of axial fibres can perform such 

 movements, it would seem that the axial fibre may be purely elastic 

 in nature, with the function of bringing the pseudopodium back to its 

 original extended position when the movements of the cytoplasmic covering 

 cease. The more actively motile flagella and cilia of the Mastigophora and 

 Ciliophora have essentially the same structure as the axopodia of Heliozoa. 

 There is an axial fibre (axoneme) covered by a thin sheath of cytoplasm. 



