BRANCH PROTOZOA: THE ONE-CELLED ANIMALS 77 



Make notes and drawings explaining these motions. 



Specimens of Vorticclla may perhaps be found dividing, 

 or two bell-shaped bodies may be found on a single stem, 

 one of the bodies being sometimes smaller than the other. 

 These two bodies have been produced by the longitudinal 

 division or fission of a single body. In this process a 

 cleft first appears at the distal end of the bell-shaped 

 body, and gradually deepens until the original body is 

 divided quite in two. The stalk divides for a very short 

 distance. One of the new bell-shaped bodies develops a 

 circlet of cilia near the stalked end. After a while it 

 breaks away and swims about by means of this basal 

 circlet of cilia. Later it settles down, becomes attached 

 by its basal end, loses its basal cilia and develops a stalk. 



4 ' Conjugation occurs sometimes, but it is unlike the 

 conjugation of Paramcceium in two important points: 

 Firstly, the conjugation is between two dissimilar forms ; 

 an ordinary large-stalked form, and a much smaller free- 

 swimming form which has originated by repeated division 

 of a large form. Secondly, the union of the two is a 

 complete and permanent fusion, the smaller being 

 absorbed into the larger. This permanent fusion of a 

 small active cell with a relatively large fixed cell, followed 

 by division of the fused mass, presents a striking analogy 

 to the process of sexual reproduction occurring in higher 

 animals. ' 



OTHER PROTOZOA 



Besides the Amoeba^ Paratncecium^ and Vorticella there 

 are thousands of other Protozoa. Most of them live in 

 water, but a few live in damp sand or moss, and some 

 live inside the bodies of other animals as parasites. Of 

 those which live in water some are marine, while others 

 are found only in fresh-water streams and lakes. 



