212 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



kinetosomes into the empty vesicle. The kinetosomes are of 

 conventional appearance and seem to be interconnected by fibrils 

 of uncertain disposition, but lack the central granules of kineto- 

 somes in the adult ciliature. The origin of these kinetosomes is in 

 doubt. Some authors (see Noirot-Timothee, 1960) consider that 

 a somatic infraciliature is present in the unciliated regions of the 

 adult body. Noirot-Timothee finds no such system in her light- 

 microscope preparations but has encountered in a very few 

 instances scattered kinetosomes beneath the body surface in thin 

 sections. Whether these are persistent somatic kinetosomes or 

 new-formed rudiments of an adoral zone anlage could not be 

 determined. The question is thus left wide open. 



An interpretation of the bewildering assortment of fibrous and 

 filamentous structures encountered in these extraordinary ciliates 

 is at best highly speculative and teleological. As noted above, the 

 body form is quite constant, only the ciliated zones and surround- 

 ing lips being notably contractile. During feeding, large plant 

 fragments may be ingested ; this requires active movement of the 

 lips and may even result in some body distortion. Bretschneider 

 considers that the retrociliary fibers must necessarily serve as 

 myonemes, since their abundance and distribution would seem 

 to qualify them for this role. In his view, the entire four-layered 

 cortex provides mechanical support and by its slightly elastic 

 properties assures recovery from distortion and causes eversion 

 of the retracted ciliated region when the myonemes relax. Noirot- 

 Timothee recognizes that the retrociliary fibers may be contractile 

 but also considers the possibility that the innermost filamentous 

 layer of the cell surface and the tracts of similar filaments coursing 

 through the body may be the myonemes, the retrociliary fibers in 

 this event serving as elastic antagonists. 



Order Hypotrichida 



The final group of ciliate protozoa is represented in the electron 

 microscope literature by its most familiar member, Euplotes, the 

 object of a detailed study by Roth (1956, 1957). Additional 

 observations on nuclear structures of Euplotes and Stylonychia have 

 been recorded in Chapter 2. 



In the hypotrichs, somatic ciliature is reduced to a small number 

 of heavy cirri (tufts of coherent cilia), typically arranged in 



