CILIATES 191 



15 m/x in diameter, that aggregate to form dorsal and ventral 

 myonemes attaching to, and presumably serving to move, the 

 holdfast. In some sections the fibrils appear to be grouped in 

 evenly-spaced parallel arrays. Elsewhere their disposition seems 

 less regular and their paths sinuous; this latter effect might 

 conceivably be a fixation artifact. De Puytorac believes that each 

 tubular fibril is composed of two or more protofibrils, about 5 m/x 

 in diameter, wound together as a helix. 



Over most of the body of the cell, a complex and orderly 

 filamentous layer separates ectoplasm from endoplasm; the fila- 

 ments originate at the bases of the kinetosomes and comprise three 

 distinct sets. Most superficially located are slender packets of 

 filaments that pass transversely to connect kinetosomes of 

 adjacent kineties. Just below these, and to the right of each 

 kinety, is a longitudinal, flattened, filamentous band. Also parallel 

 to the kineties but alternating with them are larger filamentous 

 cords. 



De Puytorac suggests that at least the external, transversely 

 oriented component of his system of filaments is comparable to 

 an ectoplasm-endoplasm boundary he has seen in other astomes, 

 and also to the filamentous boundary layer reported by Noirot- 

 Timothee in Isotricha, although no connections with kinetosomes 

 were noted by her. 



In addition to the fiber systems, de Puytorac comments on the 

 presence of abundant, tiny, rod-, disc-, or dumb-bell-shaped bodies 

 in the ectoplasm, mitochondria concentrated in the peripheral 

 endoplasm, and rather extensive arrays of concentric granular 

 endoplasmic reticulum. The remarkable structure of contractile 

 vacuole pores has been discussed in Chapter 2. 



It is particularly regrettable that ciliates of the Order Aposto- 

 matida have not been examined with the electron microscope, 

 since they exemplify with unsurpassed clarity the involved but 

 orderly processes of ciliate morphogenesis. It was largely on the 

 basis of the monographic studies of apostomes by Chatton and 

 Lwoff(1935) that the influential French school of protozoologists 

 first formulated their concepts of the importance of kinetosomes 

 in development (see LworT, 1950). The curious, symbiotic 

 thigmotrichs also have been neglected by electron microscopists. 



