THE PROTOZOA 27 



cycles are so involved and their structure with myonemes and spore 

 cases so complex that they are probably not very close to the 

 primitive stock. It is worth noting here that some authors such as 

 Ulrich (1950) have suggested that the Cnidosporidia are not 

 protozoans but metazoans. 



The Ciliophora too can be disregarded since they show par 

 excellence the extremely complex structures that can exist within 

 the protozoan cell. Thus Entodinium with its complex cirri, 

 neuromotor system, skeleton, nuclei and digestive system is 

 almost as complex as some metazoans (Fig. 5). On the other hand 

 even the most simple of the ciliophorans have a complex nuclear 

 structure. There is usually a macro- and a micro-nucleus as 

 separate bodies, though they are in the form of macro- and micro- 

 chromosomes in a single nucleus of the Chonotricha such as 

 Spirochona. In addition there is the very complex infraciliature 

 that has developed in the superficial regions of the ciliates and 

 this is more complex than that found in the flagellates. 



This then leaves two classes, the Flagellata and the Rhizopoda, 

 as the more primitive protozoans and each of these has at various 

 times been considered as the most primitive Protozoa. Thus at 

 the beginning of the century the prevalent view was that the 

 Rhizopoda were the most primitive of the Protozoa. This view 

 was well expressed by Ray Lankester (1890) in his article in the 

 Encyclopaedia Britannica. Lankester said, ' Briefly stated the 

 present writer's view is that the earliest protoplasm did not 

 possess chlorophyll and therefore did not possess the power of 

 feeding on carbonic acid. A conceivable state of things is that a 

 vast amount of albuminoids and other such compounds had been 

 brought into existence by those processes which culminated in the 

 development of the first protoplasm, and it seems therefore likely 

 enough that the first protoplasm fed on these antecedent steps in 

 its own evolution just as animals feed on organic compounds at 

 the present day, more especially as the large creeping plasmodia of 

 some Mycetozoa feed on vegetable refuse. It is indeed not 

 improbable that, apart from their elaborate fructification, the 

 Mycetozoa represent more closely than any other living forms the 

 original ancestors of the whole organic world. At a subsequent 

 stage in the history of this archaic living matter chlorophyll was 

 evolved and the power of taking carbon from carbonic acid. The 



