THE PROTOZOA 33 



suggested that it was possible to derive these two classes from 

 intermediate forms such as Mastigamoeba, and this view has been 

 followed by Grasse in his Traite de Zoologie, where he groups the 

 Flagellata and the Rhizopoda into a subphylum : the Rhizoflagellata. 

 To the groups Flagellata and Rhizopoda he gives superclass status 

 and groups such as the Dinoflagellata and the Foraminifera are 

 termed Classes. 



The Sporozoa were linked by such workers as Doflein (1916) 

 with the Flagellata and the Rhizopoda to form the group Plasmo- 

 droma. There are certain resemblances between these groups. 

 Sporozoans such as Plasmodium have both flagellate sperm and 

 amoeboid ookinetes, and spore formation is found in both the 

 Flagellata and the Rhizopoda. The Plasmodroma are then 

 separated from the Ciliophora with their complex infraciliature. 

 Yet even within the Ciliophora there are forms that are possibly 

 related to or have something in common with the Flagellata. Thus 

 Opalina is according to some writers a ciliate and according to 

 others such as Grasse it is a flagellate. 



Such close connexions between the four classes can be inter- 

 preted as showing how closely the various groups are related. But 

 there is another interpretation. Franz (1924) has suggested that 

 the Protozoa are not a strict phylum but instead are a grade of 

 organisation. He thinks that there is no good evidence that the 

 Protozoa are more primitive than the Metazoa and states that 

 the unicellular forms could have been derived many times from 

 the Fungi, Algae and the Metazoa. The various groups such as the 

 Flagellata, Rhizopoda, Sporozoa or Cilophora would then each be 

 polyphyletic and contain animals that have been derived from 

 different sources at different times but which are grouped together 

 because they have certain convergent morphological characteristics. 



The view that the four classes are polyphyletic is discussed by 

 Hyman (1940). " The flagellates themselves appear to be a hetero- 

 geneous assembly of groupsthat have probably arisen from a number 

 of different sources, possibly bacteria and spirochaetes, many of 

 which are provided with flagella. . . . The rhizopods like the 

 flagellates constitute an arbitrary assemblage of forms having in 

 common the pseudopodial method of locomotion and food capture. 

 It is probable that the various orders of rhizopods have arisen inde- 

 pendently from the different groups of flagellates, i.e. the class is 



