THE CLASSIFICATION OF PROTOZOA 79 



is no evidence. As Dobell wrote in 191 1 of this universal 

 parent : 



* Concerning this fabulous " amoeba " we know nothing, 

 save that its correct systematic position is probably in the 

 group which contains the centaur, the phoenix, and the 

 hippogriff.' 



If the Protozoa are indeed the first animals, one can be fairly 

 confident that the primitive form was flagellate rather than 

 amoeboid, for it is the flagellate forms which connect most closely 

 with plants. 



The group Protozoa is a phylum, but it is sometimes also raised 

 to the rank of a sub-kingdom, the only other sub-kingdoms being 

 the Parazoa or sponges (p. S8), and the Metazoa, including all 

 other animals. All modern writers are agreed on the main divisions 

 of the Protozoa, but there is some variation in the names used. 



CLASS L—MASTIGOPHORA 



Protozoa which are predominantly flagellate although they 

 may form pseudopodia. It is best to avoid the name Flagellata as 

 a title for this group, since the word is used by botanists with a 

 different and wider connotation. There are two sub-classes — 

 Phytomastigina, which possess chlorophyll or closely resemble 

 forms which do; and Zoomastigina, which neither possess chloro- 

 phyll themselves, nor resemble forms which do. Most of the 

 Phytomastigina, such as Polytoma and Eiiglena, are on the border 

 line between the animal and plant kingdoms ; others, such as 

 Chlamydomonas, have no claim to be called animals, and are only 

 included, by some zoologists, as Mastigophora because of their 

 structural similarity to colourless forms. The biochemistry of the 

 sub-class is diverse, which suggests that they are not closely 

 related to each other, and there is some evidence that they are 

 degenerate Algae. The Zoomastigina, on the other hand, are 

 entirely animal in nature, and have little or nothing in common 

 with the Phytomastigina except flagella. In only one genus is any 

 trace of a syngamous process known. Many have a somewhat 

 compHcated internal structure of nuclei, skeletal rods, conducting 

 threads and so on, and many also have several flagella. Trypano- 

 soma is an example with one flagellum. Trichomonas, parasitic in 

 the gut, has several. 



