CHAPTER 7 



CONCLUSIONS 



In the foregoing pages we have surveyed, in a necessarily cursory 

 manner, a formidable body of information on protozoan 

 ultrastructure. Yet one need but glance at any textbook of 

 protozoology to appreciate how small a sample has been selected 

 from the legions of existing species. And for very few of those 

 studied is the available information anything like complete — as 

 the workers who have investigated them are the first to point out. 

 How can we presume to draw conclusions from data that are 

 fragmentary, scattered, and based almost exclusively on observa- 

 tions of micromorphologic appearance unsubstantiated by 

 evidence from any other quarter ? It must be admitted — in fact, 

 insisted — that the effort is presumptuous and that it can consist 

 only of a summing-up of impressions, inferences, and intuitions. 

 Impressions concerning organelles with a wide distribution in 

 nature seem the least precarious and have already been presented 

 in Chapter 2. For the most part they do not need reiteration. 

 Other speculative considerations have been sprinkled through the 

 discussions of various groups. In this chapter are considered, 

 first, some of the novel structures repeatedly encountered in 

 protozoa; perhaps their distribution offers clues to their signifi- 

 cance. Then we may inquire whether the facts of ultrastructure 

 provide any new insights into relationships among protozoa and 

 other organisms. 



Membrane Differentiations 



Almost all protozoa examined prove to have a unit membrane 

 at the actual cytoplasmic surface. Possible exceptions include 

 Gromia, where a highly organized lamella is found immediately 

 under the shell, and no conventional plasma membrane is apparent 

 in the material studied. In heliozoa and filose rhizopods the 

 existence of a semipermanent membrane over adjacent antagonistic 



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