4 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



These authors argue that such similarities may be the result of 

 inescapable convergence. Recognizing the inventiveness of living 

 matter and the fixity of physical laws, they suggest that totally 

 unrelated stocks of primitive organisms could have hit upon the 

 same solutions — the only possible solutions — to the problems 

 of survival and reproduction. 



The decision whether a ubiquitous solution is the only 

 possible one or instead one that, at the time of its invention, gave 

 its possessors a literally overwhelming selective advantage will 

 require a far deeper understanding of biological evidence than 

 we now possess. At present the same deductive arguments can 

 be piled up on both sides of the fence. Chloroplasts, mitochondria, 

 Golgi elements, nuclear membranes, flagella, centrioles — all 

 show an impressive universality of structure. They are morpho- 

 logical expressions of ubiquitous solutions to problems that we 

 can define only in general terms. Are they the results of a common 

 genetic heritage or of repetitive, independent, evolutionary events ? 

 The study of protistan comparative morphology can at the very 

 least contribute circumstantial evidence toward an answer. 



To consider all the implications of protozoan ultrastructure 

 would require a review of the whole field of cell biology, as well 

 as of all protozoology. The author disclaims any such ambition 

 and recommends as sources of relevant information competent 

 reviews and treatises in cell biology and ultrastructure such as 

 those by Brachet (1957), Picken (1960), and numerous authors 

 under the editorship of Palay (1958) and of Brachet and Mirsky 

 (1959 et seq.) t and in protozoology those by Grasse and others 

 (Grasse, 1952, 1953), Hyman (1940), Hall (1953), Kudo (4th ed., 

 1954), Smith (1955), Grell (1956), and Schussnig (1960). It hardly 

 needs emphasizing that the work to be reviewed here would be 

 meaningless without the solid edifice of light-microscope studies 

 in protozoology to support it. 



Argument over the limits of the unnatural "Phylum Protozoa" 

 will be evaded by accepting as protozoa all those organisms so 

 recognized in Volume I of the Traite de Zoologie (Grasse, 1952, 

 1953) and by following the classification proposed therein (except 

 that uniform endings for taxon names, as specified by Hall, 1953, 

 will be imposed on Grasse's system; see Appendix). The author 

 recognizes (as does Grasse) that this delimitation arbitrarily cuts 



