19 



The general method of reproduction is by simple fission. 



The Protozoa are the lowest group in the Animal King- 

 don ; they are the first animals, as their name implies, 

 and, among them are the most primitive forms of animal 

 ?ife known. 



Describe the General Features of the Protozoa. 



The cell may be naked or may have a firm envelope. 

 The outer portion (ectoplasm) is clearer and of a firmer 

 consistency than the inner mass (endoplasm), which is 

 opaque, ^granular, and more or less fluid.- There may be 

 only one nucleus, or two, or more ; food vacuoles and 

 contractile vacuoles are generally present. 



The structure of the cell is often complex ; for instance, 

 the ectoplasm forms special locomotor cilia and flagella, 

 trichocysts with eversible stinging threads, muscle fibrilla}, 

 and tests or skeletons often wonderfully intricate. 



A remarkable feature is the specialisation of the nuclear 

 structure into separate nuclei with distinct functions. 



The mode of feeding may be holozoic, holophytic, 

 saprophytic, or parasitic ; some species are both holozoic 

 and holophytio or saprophytio. 



Reproduction is asexual by fission, either simple division 

 into two individuals or multiple resulting in many (e.g., 

 schizogony in Sporozoa). A sexual method, temporary 

 union or permanent conjugation of two individuals (gam- 

 etes^, also occurs. 



In several instances the life history shows alternation of 

 generations. 



There are four chief types of Protozoa : 



1. The Rhizopod or Amoeba Type. Body naked* Tem- 

 porary protrusions of the protoplasm (blunt lobopods or 

 thread-like pseudopodia) serving for slow movement and 

 for securing food. 



2. The Flagellate type. Body naked or covered with 

 a cuticle, and provided with one or more flagella for active 

 movement. 



