THE PROTOZOA 31 



invented or produced chlorophyll. Accordingly I incline to the 

 view that chlorophyll as we now know it is a definitely later 

 evolution — an apparatus to which protoplasm attained, and as a 

 consequence of that attainment we have the arborescent, filamentous, 

 foliaceous, fixed series of living things we call plants. But before 

 protoplasm possessed chlorophyll it had a history. It had in the 

 course of that history to develop the nucleus with its complex mecha- 

 nism of chromosomes, and it had during that period to feed." 



There is a second reason why the Flagellata are sometimes 

 considered to be more primitive than the Rhizopoda. During their 

 young stage some of the Rhizopoda such as Naegleria and 

 Dimorpha show a flagellate condition which is considered by some 

 investigators to be a form of recapitulation; i.e. the young stage 

 shows more primitive characteristics than those present in the 

 adult. How much faith can one have in this type of argument? 

 We know that certain flagellates such as Mastigamoeba show 

 pseudopodia as well as flagella and thus the presence or absence of 

 pseudopodia or flagella does not necessarily indicate primitive- 

 ness. What is more important is the concept that these Rhizopoda 

 show the flagellate stage only in the young forms and that there- 

 fore the flagella are more primitive than the pseudopodia. 



We are lucky in that there has been a recent investigation by 

 Willmer (1956, 1958) into the factors that determine the acquisi- 

 tion of flagella by the amoeba Naegleria gruberi. Willmer showed 

 that the amoeboid Naegleria can be made to turn into a flagellate 

 form with one to four flagella by placing it in water. The change 

 takes from 20 min to 24 hr to complete and during this time 

 is accompanied by the development of a definite antero-posterior 

 axis in the cell; the flagella appearing at the anterior end. The 

 pseudopodia can develop from any part of the animal. The 

 presence of salts such as lithium chloride, magnesium chloride 

 and magnesium sulphate suppress the development of the 

 flagella but leave the pseudopodia fully active. The change from 

 amoeboid to flagellate condition is reversible and depends upon 

 the environmental conditions (Fig. 6). This means that the 

 flagellate condition is not necessarily found in the young animal ; 

 either stage can reproduce and either stage can be found in the 

 young animal. Bunting (1926) showed that the rhizopod Tetramitus 

 could undergo cell division in either the amoeboid or the flagellate 



