PROTOZOA AS CELLS 49 



flagellates (Chapter 4) and in trypanosomes (Chapter 5). Double 

 kinetosomes often are shown in figures of these species but are 

 interpreted as early division stages. We might say that kineto- 

 somes prefer to come in pairs, but that they presumably can 

 function temporarily, in the non-dividing cell, as single units. It 

 is noteworthy in this connection that Mazia, Harris, and Bibring 

 (1960) have demonstrated that the mitotic centers of echinoderm 

 eggs are normally always duplex, but that the two components 

 can be forced experimentally to separate and function singly as 

 mitotic poles. 



The discovery of the 9/9 + 2 pattern surely is one of the most 

 provocative that electron microscopy has yielded. The universal 

 occurrence of an unvarying geometric configuration at such a 

 relatively gross multi-macromolecular level is without parallel. 

 Unlike some other exciting ultrastructural generalizations that 

 coincide satisfactorily with models previously conceived by 

 biophysicists or at least invite rational interpretation, this one 

 remains to date an almost complete enigma. 



The most primitive protists known, the Monera, lack both 

 centrioles and true flagella (pecilokonts) as well as membrane- 

 limited nuclei, mitochondria, Golgi elements, and intracellular 

 fiber complexes. Development of such discrete organelles to 

 carry out the multiple assignments of cell metabolism in a manner 

 efficient enough to allow larger cell size and greater structural 

 elaboration than are achieved at the moneran level undoubtedly 

 occupied a long and hectic chapter in the ancient history of life. 

 One can only guess when in this period the kinetosome/centriole 

 evolved (see Chapter 4), and whether its primary function was 

 flagellar locomotion or nuclear division. Certainly it could only 

 have been perfected by a cell in which mechanisms for the 

 transmission of information from one generation to the next had 

 reached a high level of precision. 



Grimstone (1959b) proposes that flagella may have evolved 

 independently in several groups, sharing a common structure 

 down to its minutest details because no other can fulfill the 

 mechanical and developmental requirements of such an organelle. 

 But whether it evolved once or several times, the 9/9+2 pattern 

 would hardly have been perpetuated so faithfully without good 



