THE PROTOZOA 29 



1 green ' plants were rendered possible by the evolution of 

 chlorophyll, but through what ancestral forms they took their 

 origin or whether more than once, i.e. by more than one branch, 

 it is difficult even to guess. The green Flagellate Protozoa 

 (Volvocinae) certainly furnish a connecting point by which it is 

 possible to link on the pedigree of green plants to the primitive 

 protoplasm; it is noteworthy that they cannot be considered as 

 very primitive and are indeed highly specialised forms as compared 

 with the naked protoplasm of the Mycetozoon's plasmodium. 

 Thus we are led to entertain the paradox that though the animal is 

 dependent on the plant for its food yet the animal preceded the 

 plant in evolution, and we look among the lower Protozoa and not 

 among the lower Protophyta for the nearest representatives of that 

 first protoplasm which was the result of a long and gradual 

 evolution of chemical structure and the starting point of the 

 development of organic form." 



If one consults any of the older texts such as those of Lankester 

 (1909), Delage and Herouard (1896) or Kukenthal and Krumbach 

 (1923) one finds that the Rhizopoda are placed as the first class of 

 the Protozoa. 



The accent of protozoan research changed during the first 

 part of the twentieth century. Instead of being concerned with the 

 morphology and life cycles of the Protozoa, the interest became 

 more centred upon the physiology and in particular the nutritional 

 requirements of the Protozoa. This change in accent from a 

 morphological one to a physiological one may explain the change 

 that took place in the prevalent attitude to the phylogeny of the 

 Protozoa. In such texts as those of Hyman (1940) or Grasse 

 (1952) the Flagellata take pride of place over the Rhizopoda; the 

 Flagellata being the first class to be described. It should, however, 

 be noted that Klebs in 1892 suggested that the Flagellata were in 

 fact more primitive than the Rhizopoda. 



Grasse points out that since many of the members of the 

 Flagellata possess chlorophyll they are able to undertake synthesis 

 of all their food requirements without the assistance of any 

 complex compounds. This view is much the same as that of 

 Pringsheim (1948), who showed that many of the colourless 

 flagellates such as Astasia or Polytoma can be found in pure 

 cultures of Euglena and Chlamydomonas respectively. The 



