30 THE PROTOZOA 



coloured forms gave rise to the colourless forms, i.e. Astasia is a 

 colourless Euglena, and hence the groups Astasia and Polytoma 

 are not strict monophyletic genera but instead are polyphyletic 

 grades. Pringsheim suggests that many of the present-day colour- 

 less flagellates are derived from the coloured form and this would 

 make the coloured forms more primitive than the colourless forms 

 (Pringsheim and Hovasse 1950). 



Lwoff (1944) in his book on physiological evolution goes even 

 further and contends that from a physiological point of view 

 evolution is retrogressive. The most primitive Protozoa, he states, 

 must surely have been entirely self-supporting with little or no 

 food requirements, but as evolution occurred the cells lost their 

 synthetic ability and became more and more dependent upon other 

 cells for the provision of their food requirements; i.e. they 

 regressed instead of progressed. 



There appears to be a fallacy in LwofT's argument. The fact 

 that a cell has minimal food requirements does not mean that this 

 is necessarily the most primitive condition. In fact most of the 

 schemes suggested for the origin of living material place the 

 advent of chlorophyll at a very late stage in the evolutionary 

 sequence, the plant cells having the chlorophyll system super- 

 imposed on the anaerobic metabolic system (Oparin 1957). The 

 very earliest living forms would have had considerable food re- 

 quirements. It would be perfectly possible for a sarcodine-like 

 form to be the most primitive animal feeding on amino-acids and 

 carbohydrates synthesised by abiogenic methods. The presence 

 of chlorophyll is indeed a good reason for considering the Flagellata 

 as an advanced group of the Protozoa. This view was in fact 

 suggested by Lankester in 1909. 



Lankester stated, " The real question ... is whether we find 

 reason to suppose that the combination of carbon and nitrogen 

 to build up proteid, and so protoplasm, required in the earliest 

 state of the earth's surface, the action of sunlight and the chloro- 

 phyll screen. We must remember that these are now necessary 

 for the purpose of raising carbon, and indirectly nitrogen, from the 

 mineral resting state to the high elaboration of the organic molecule, 

 yet it is, after all, living protoplasm which effects this marvel with 

 their assistance ; and it seems (though possibly there are some who 

 would deny this) that it is protoplasm which has, so as to speak, 



