ZOOFLAGELLATES 163 



features, and here, so far as we know, the answer has been rather 

 different, since nuclei seem to have given up any morphological 

 association with kinetosomes at any stage, and no centrioles are 

 known. 



Superorder Opalinica 



The opalinids are protozoa symbiotic in the guts of cold- 

 blooded vertebrates ; they have a uniform covering of body cilia, 

 no mouth, many equivalent nuclei, and no centrioles. The long 

 accepted practice of classifying them as protociliates has recently 

 fallen into disfavor. Grasse (1952), following the lead of several 

 other workers, places them in the Superorder Opalinica of the 

 Class Zooflagellatea. Corliss (1955) in a more recent discussion 

 of the puzzle, favors a recognition of flagellate affinities but 

 objects to the implication that their position is equivalent to the 

 superorders Protomonadica and Metamonadica. In the most 

 recent critical light-microscope study of opalinid life cycles and 

 morphogenesis, Wessenberg (1961) finds that they share about 

 equal numbers of characteristics with the flagellates and with the 

 ciliates, in a combination that is unique to them. He feels that it 

 is unjustifiable to class them with either group. 



Opalinids have been examined with the electron microscope 

 by Bretschneider (1950), Pitelka (1956), and Blanckart (1957) and 

 finally by Noirot-Timothee (1958d, 1959), whose excellent micro- 

 graphs provide most of the information for the following 

 description. Various species of Opalina have been included in 

 the studies, but no specific differences in ultrastructure are 

 apparent. Opalina is elongate, obliquely rounded at the anterior 

 end, and tapers to a point posteriorly. It is strongly flattened 

 laterally (according to Wessenberg; some other authors have 

 considered the flattening to be dor so-ventral). Along the oblique 

 anterior margin a row or narrow field of kinetosomes occurs, 

 extending part way down the ventral edge. From this field, 

 called the falx, orderly rows of kinetosomes extend posteriad, 

 providing the lateral surfaces with a more or less uniform 

 covering of short cilia. Each longitudinal row of kinetosomes 

 is called a kinety. Some kineties extend to the posterior end of 

 the cell, while others end at any level short of this. 



The electron microscope reveals that the entire surface of 



