CONCLUSIONS 227 



either normal metachrony or ciliary responses to stimuli over the 

 general body surface; hence the membrane-transmission theory 

 gains plausibility by default. Oral ciliature is something else 

 again, since there are usually enough interconnecting elements to 

 accommodate any theory, if one is not particular about details of 

 experimental proof. The greatest obstacle to immediate progress 

 is the almost prohibitive difficulty of determining by electron 

 microscopy what ultrastructural constituents have and have not 

 been altered by experimental manipulation, at least with the 

 techniques devised to date. 



A serious consideration of ciliary coordination would require 

 scrutiny of metazoan systems and much more space than is 

 available here — we can only acknowledge the problem. 



Many of the fibrillar structures of protozoa are so placed as to 

 make very tempting the idea that they could serve in the establish- 

 ment and maintenance of spatial relationships, if one assumes that 

 activities or states in the kinetosome could trigger activities or 

 states in whatever is present at the opposite end of the fibril. In 

 the complete absence of developmental studies of ultrastructure, 

 such an idea remains tenuous ; we have no way of distinguishing 

 symptoms from causes. 



Protozoan Relationships 



The contribution of electron microscopy to protozoan taxonomy 

 already is considerable. Among phytoflagellates that have so 

 little microscopically visible structure at all, such properties as 

 scale pattern and the number and morphology of nagella have 

 justified revisions of generic and even familial and ordinal 

 classification. The discovery of peculiar anterior organelles in 

 several sporozoa clearly indicates the value of ultrastructural 

 studies here. Of the larger and more complex protozoa, not 

 enough species have been studied to suggest any modification of 

 already abundant morphologic criteria. Among the euglenoids, 

 trypanosomids, bodonids, gymnostomes, hymenostomes, hetero- 

 trichs, and entodiniomorphs, related genera have shown such 

 similarities as one would expect. 



As for detective work in the field of phylogenetic relationships 

 among larger categories, it seems that, at the lower end of the 

 scale, the biochemists will continue to have most of the fun. 



