PHYLUM PROTOZOA 



29 



The individual cells in many colonies are not bound closely 

 together but are loosely associated by protoplasmic connections 

 (Fig. 14) or by individual stalks of attachment. The appearance 

 of unity is greatly strengthened in many colonies by the presence 

 of a regularly shaped gelatinous mass (Fig. 5) in which the 

 cells are embedded. Branching or arboroid colonies (Fig. 14) 

 frequently occur in the Peritricha and in some Mastigophora. 

 Highly developed colonies (Fig. 5) are 

 common in the Mastigophora, especially 

 among the Euglenoidea. Because of 

 the similarity between various masti- 

 gophoran colonies and the cleavage and 

 blastula stages in the development of 

 Metazoa, this group has frequently 

 been cited as the one most directly in 

 line with metazoan phylogeny. How- 

 ever, some workers are inclined to the 

 view that while colony formation is less 

 characteristic of the Ciliata, speciahza- 

 tions found there demand consideration ch^ytomo7ad?na°^ ^"^mnlblyol 



in any discussion of the phylogeny of seHularia Ehrenberg. A, ar- 

 ii ^ T\/r^+^ ^„ rangement of cells in treelike 



the Metazoa. ,„l„^y. ^ individual in its 



The general plan of classification by cuplike sheath. {From Shuii, 

 Doflein has been adopted in the ^?^f"'' °"^ ^"'^'"' ''^''' 

 present work. In this system, relation- 

 ships are more clearly shown than in the older systems which 

 involve recognition of four equivalent classes. In the remainder 

 of this chapter, the following subphyla and their included classes 

 are discussed: 



Subphylum I. 



Class 1. 



Class 2. 



Class 3. 

 Subphj'lum II. 



Class 4. 



Class 5. 



Plasmodroma. 



Mastigophora. 



Sarcodina. 



Sporozoa. 



Ciliophora. 



Ciliata. 



Suctoria. 



SUBPHYLUM PLASMODROMA 



In the subphylum Plasmodroma are assembled all Protozoa 

 which never develop cilia, while the subphylum Ciliophora 

 includes those which have cilia at least during part of their 

 existence. 



