DISTINCTIVE CHARACTERS OF THE PROTOZOA 11 



always by some form of fission that is to say, division of the body 

 into smaller parts ; that the phenomena known as "syngamy " and 

 " sex " occur, perhaps universally, throughout the group ; and that 

 it is very characteristic of 

 Protozoa, as compared with 

 other Protista, to exhibit in 

 their life-history a develop- 

 mental cycle, more or less 

 complicated, in the course of 

 which the organism may appear 

 under very different forms at 

 different stages in its develop- 

 ment. 



The Protozoa, as thus under- 

 stood, are commonly divided 

 into four main subdivisions, 

 termed "classes." Other 

 methods of classifying the 

 Protozoa have been suggested, 

 which will be considered later ; 

 for the present the old- 

 established subdivisions are 

 sufficient for our purpose. 



CLASS I., SARCODINA.* 

 Protozoa in which the proto- 

 plasmic body is naked or non- 

 corticate that is to say, 

 without a limiting envelope 

 in the form of a cuticle, 

 membrane, or stiff xjortical 

 layer ; consequently the body 

 tends to be either more or less 

 spherical in floating forms, or 

 to have an irregular, con- 

 tinually changing shape in 

 creeping forms. Organs serving 

 for locomotion and capture of 

 food are furnished by tem- 

 porary extensions of the living 

 protoplasm, termed pseudo- 

 podia. A skeleton or shell 

 may be present. Examples 



FIG. 10. Acineta grandis. si., Stalk ; th., 

 theca ; s., suctorial tentacles. After 

 Saville Kent. 



* The name is derived from sarcode, the term coined by Dujardin to denote 

 the living substance, subsequently named by von Mohl protoplasm, the term now 

 universally employed. 



