16 PROTOZOA. FORAM1NIFERA 



pseudopodia are seldom present, but the surface is provided 

 with cilia or flag ella, which are fine threads of protoplasm 

 having a definite form and a rhythmic movement. 



Reproduction in the Protozoa takes place usually by 

 fission (i.e. division into two parts) and sometimes by the 

 formation of spores. In some cases conjugation of two 

 or more individuals occurs, representing to some extent 

 sexual reproduction. In some of the Protozoa there is 

 no skeleton, but in others a shell is formed. 



The Protozoa can be divided into four main groups, 

 (1) the Gymnomyxa, (2) the Flagellata, (3) the Infusoria, 

 (4) the Sporozoa ; no examples of the last three divisions 

 have been definitely recognised in the fossil state. 



CLASS I. GYMNOMYXA (SARCODINA) 



The members of this group possess no external mem- 

 brane (cuticle), and are able to throw out pseudopodia, 

 by means of which movement takes place and food is 

 obtained. 



The Gymnomyxa or Sarcodina are divided into several 

 orders, of which only two have been found fossil, namely, 

 the Foraminifera and the Radiolaria. 



ORDER I. FORAMINIFERA 



The Foraminifera are characterised by their thread-like 

 pseudopodia, which frequently branch and anastomose ; 

 and by possessing in most cases a shell or test, which may 

 be calcareous, arenaceous, or chitinous. 



The calcareous forms are by far the commonest, and 

 in these, two kinds of shell may be distinguished, namely, 

 the vitreous and the -porcellanous. In the vitreous, the 



